the MPC series by Akai, as near as I can tell by reading (don't own one) are basically the guts of a keyboard workstation (such as the Triton, Fantom, XP series from Roland, etc) only without a set of keys to play. That means that you have to have a separate keyboard controller or another MIDI keyboard to be able to play the sounds.
I'm not sure what you mean by "synth rack", sounds like another soft synth program?
The main advantage to a "keyboard workstation" such as the Triton is that you have everything you need to compose, all in one box that will fit in a roadcase and can be tossed in the trunk along with a set of phones when you go to the wife's relatives for an extended visit and you have nothing in common with them (oops, did I say that out loud? :=))
Software versions of synths, samplers, and sound modules can be just as good as the hardware versions, even better if you have high end sound cards on the computer(s) you're running them on.
All DSP (Digital Signal Processing) takes (duh) computing horsepower, so there is a limit to how many voices can be output from any given computer running such software. Up to that limit, everything is fine, other than usually everything that's playing has to come out of the same set of outputs. This limits the creative mixing/effects you can do to individual tracks.
If you were going to do everything with soft synths/samplers, you would tend to run out of computing power before you were happy with the sound of a mix IMO - there's something about everything coming out of the same box that is just too "same", somehow, and dealing with that problem would take some seriously different software or thought if you're doing everything in a computer.
My own approach to this, based on using the stuff primarily in a studio environment, is a dedicated keyboard controller AND a workstation, hardware modules/keyboards for the "bread and butter" stuff (things you use ALL the time) and a monster computer running something like Sonar for sequencing/soft synths, with a separate (but synced) monster computer for a hard disk recording package (I use Samplitude Producer) - All this will soon be interfaced with
a Tascam DM-24 digital mixer, as soon as I find an acceptable multi-channel digital interface that talks Tascam protocol. the mixer doubles as a hardware control surface for Sonar and Samplitude, so everything can be automated with automation info stored with the project file instead of in the mixer.
For portability, I have
a Roland XP-50 workstation which gets plugged into an 8 port MIDI interface when in the studio. Out of the studio, it plugs into a Roland UA-100, which is a USB midi and sound card box for laptops, which also has some guitar EFX and a better quality set of converters than my laptop has.
The XP-50 can also stand alone for any MIDI production - it has its own floppy for storing sequence info, and can save things as Standard Midi files. I can then plug the resultant floppy into the studio computer and have Sonar expand the SMF into separate channels per track for additional tweaks or adding audio tracks. I can also do that into the laptop and add audio tracks thru the UA-100, although the laptop isn't powerful enough for more than about 8-10 tracks.
By "vintage racks", I'll assume you mean racks with physical, vintage processing gear in them? If so, that depends on which pieces of gear you're talking about. There are compressors, gates, EQ's, mic pre's, almost anything you can think of, from days past that can be found on Ebay, in garage sales, old studios, widows selling hubby's goodies, etc, each of which has its own unique sound. Some are great, some are crap, some crap SOUNDS great when used on the right track, etc.
Some of these vintage sounds have been cloned in software, with varying degrees of success. Some people only want "the original", even if the clone works well.
Preamps generally are NOT cloned, at least not much and not very successfully. Each mic has a different characteristic sound, and so do preamps. Some are very neutral, and sound like whatever mic you feed into them while others have a very characteristic sound and work well for specific types of tracks. If you want a variety of real sounds to complement different mics/instruments/vocalists, a few different types of preamps in a "vintage rack" would give you some choices.
Hope that helped some, at least it's a start... Steve
