Software is a all pretty good these days, some better than others, but it's more likely that a combination of hardware and knowledge/experience deficiancies are the root cause. I'd suggest you work from the source to the mix, one link at a time, and find out where the water gets muddy. First, does what you're recording sound good, or are you expecting the recording process to make it sound good? It won't. This sounds self evident, but you'd be supprised at the number of people who record dead strings, and other crappy sounds, and wonder why the recording sucks.
Second, what does it sound like coming out of the PA, before it goes into the soundcard? Use headphones and see if what's coming out of the PA sounds like something you want to record. If not, then you need to determine if it's the PA or the mic, or your mic technique that's the problem. If so, move on to evaluating your soundcard. This is almost certainly a sonic bottleneck in your system right now, and I highly recommend you consider an upgrade there. But try just recording a single track and playing it back, and A/B it with what you're sending in (out of the PA). If it sounds ok, then it may be what your doing in the software that is mucking up your sound.
It is probably a combination of all these things that's leaving your end result a bit flat, and you'll need to tackle them one at a time (or all at once if you can write the check). All except experience and knowledge, which you'll have to aquire the usual way.
Good luck.