I have no experience with Eureka so have no real opinion concerning it specifically. If the Eureka seems to substantially improve your recordings, either the way you had things connected was really, really not quite right or what it offers matches the 'sound' for which you're searching exactly. You've reduced flexibility, locked in options to something that appears to work for you . . . and there is no way anyone but you could have an effective opinion regarding that. We might, if we've used it, have an opinion about the 'grain' of it's EQ, the transparency of the pre, how effective the compressor is for different genre's but it is doubtful that it offers anything (except specific 'color') not readily available via software . . . thus how well it might match your needs is entirely aesthetically subjective.
A fairly standard approach, particularly as one is just starting, to digital recording is to track as 'dry' as possible. That is inject as few things that alter or color the source prior to initial analog to digital conversion (A/D) as possible. With a certain amount of care a digital file can be processed an intractable, if not infinite, number of ways and times without destroying ability to return to pristine state. But anything injected between source and initial A/D is permanent. There are times when, with experience, efficiency suggests making some decisions, altering the initial source prior to A/D . . . trade off being efficiency with flexibility
Generally speaking, depending on specific goals, a transparent mic pre is a good place to start. The most important part(s) of any recording gear will, for foreseeable future, be the analog elements. They are also the most expensive and require the greatest skill when assembling a finished unit. The EQ and compression in the Eureka might be useful over the long haul but there are a lot of decent plug in's with eq and compression at least as good as, frequently with more options and better UI's then any entry level hardware. Entry level hardware seldom aspires to or achieves transparent effect (that is altering only the single thing it is 'labeled' to achieve)
Even before pursuing a more transparent, and/or better, mic pre (then those in the Presonus interface) picking up some better mic's might be a useful strategy. And in bang for buck don't over look some of the dynamics. I don't have the love affair with the Shure SM57 that some do but it has a deserved work horse reputation: perhaps not perfect for anything but useable on a lot: snare, hats, cymbals, amps, etc. In a number of areas where SM57 is weak the Sennheiser 421MD can shine: kick drum, bass cabs, horns, vocals, toms, hand percussion, I've been OK with it (primarily in live settings) on acoustic guitar. A SM57, 421MD pair works quite nicely on a lot of guitar cabinets. Picking up an SM7 as a vocal mic can, depending on voice and content, get better results then pursuing an succession of cheap condensers.
Depending on which condenser you have while investing in a 'mod' will not do much for it's cache resale value can transform a so-so mic into something you will never want to sell.
But all of this simply skirts the edges of the central issue, with regard to things you seem to want to improve in your recordings. If you are recording in ambient space the next most important variable, after content, performance, quality of instruments, is that 'space'. Recording in small rooms with parallel surfaces can be difficult (if not disastrous) no matter what ancillary (e.g. A/D) gear you have. Better gear can in fact illustrate weaknesses in the room ever more faithfully. There are things you can do to compensate for less then perfect rooms (sort of the heart of a home recording forum) but they all involve compromises. And the compromises will, of necessity, be unique to your goals.
Generally speaking it is easier to compensate on the recording side, then the mixing side . . . you spend time, effort, money, making the music sound as good as you can, but that effort does not translate, applies to only a single spot in a single location, when working in poor, indifferent rooms . . . this is why, with regard to recording, the general consensus is that most cost effective thing you can do is work on the 'space', the rooms in which you record and mix.
now unfortunately, even though much of the entry level cost for gear is lower then it was when I started, to record you not only need acceptable space, but a minimum quality level in the gear. And almost no one, ever, has enough funds to everything all at once. Thus the general advice: decent mic(s), transparent mic pre, start learning something about physics of pressure waves in 3D space, so adjustments done to space in which you record and mix stand a chance of actually improving things. All of this tends to be easier then it used to be, but there is a lot of less then useful gear, a lot of less then useful opinion
For example I know what I mean by 'presence' in a music voice (can be any instrument but 'presence' usually depends on a coherent harmonic sequence) but to be honest not entirely sure what you mean, except I suspect it is different then what I mean. So unless we are talking about the same thing with that one word my opinion regarding it is pretty useless to you.
Finally there is a lot of software out there, some of it priced pretty conveniently. You just have to demo stuff until you find the pieces that work for you. If you're not comfortable with 'feel' of Cubase try Audacity . . . its free. Personally even though SAW and Samplitude were some of my first legitimate software DAW's I'm pretty happy with Reaper . . . and gradually I'm getting fewer 'funny' looks when I mention it among the elite coffee klatch clusters of 'pros' in which I'm occasionally compelled to talk. Saw a similar arc with Cool Edit (back in early to mid '90's) (now Audition) . . . and I still use AA 3 as editor of choice. I think in the past year I've used all the main names (except perhaps Samplitude) they all do pretty much the same thing, each have strengths and weaknesses you just have to sort out which seems to be match the way you work. Each one will have (at least) one or two seemingly non intuitive elements . . . that nothing but practice and patience will elucidate. But you have to make some recordings before you sort out what does not work. (in some ways more important then trying to guess what does work.
really lastly, none of the stuff here in 'new' to this or any of the other forums . . . But even that opinion can be gleaned from a host of other posts. Spending some time searching and reviewing earlier posts can place any posters opinions within a context that lets you 'parse' them more accurately. For example I might have had a bad experience with Presonus customer service & and now hate them . . . my experience does not discredit my opinion but it does color it . . .
general homilies, aphorisms might not seem all that useful but things that are purely aesthetically subjective can frequently only be responded to with biased opinion or very, very generally. Personally I think, depending on your disposable income, you money could be disposed of more effectively then on the Eureka, but without knowing a lot more about your gear list, your goals, that opinion is not really worth the effort to type it.
in any case good luck
