i did some a/b comparisons of the pres in my collection a while back and heres a summary for you that may help
digi 002 console, digi 003 rack, presonus digimax 96k, and a mackie onyx 800r, the brick, art mpa gold, art v3 tube mp, mbox 2
all pres tested with a u87, and audio technica 4047, an sm57, and a senn 421
results rundown:
1-great river - always sounded the best against the other pres. most depth, best low end response, never sounds fizzy or harsh. I wish i would have got one of these when i started recording. amazing on everything, especially bass and vocals. i wish i had a board with 24 of these things. very punchy. makes any mic you have sound 1000% better, 57s can be used on guitars again!
2- two way tie
onyx 800r/art mpa gold
onyx 800r - 8 channels, very clear, not over hyped, very versitile, good clean response that works well on drums and guitars. great dynamics and headroom
art mpa gold - 2 channels, upgraded cheap stock tubes(very easy) tons of variety in sound. great for getting nice tube clipping. has lots and lots of things to toy around with, mic impedance, plate voltage, tube saturation. sounds awesome awesome on snare drum, kick drum, vox(with high plate voltage), and clean guitars. all around great performer. easy to use
3 - groove tubes "the brick" - a little low on the gain side. upgraded the tubes. super awesome on bass and aggressive vocals. cool on acoustic guitar, crappy on a kick drum. implies a heavy "tube sound" on the signal(reduced extreme highs and lows, compressed mid range). very useful and relatively cheap.
5 - digi 003 rack internal pres/
digi 003 - decent overall pres, does not have the depth of of the mackie or great river but can be useful for things like toms or maybe guitars. not a bad pre but not spectacular. would always use the mackie before the digi 003
6 - presonus digimax - another decent pre. kind of harsh and fizzy but much better than a lot of stock board pres(mbox 2 and digi 002 im pointing at you). lacks a super clear low end but still very acceptable. sounds good better with dynamics than condensers, no go for ribbon mics. probably would not buy again and only use in a pinch.
7 - tie for last place
digi 002 - very flat(boring) sounding. no low end or punch. bad for vocals or anything that will be the focus of your mix. can be very harsh and nasally. dislike the most. good for demos. very noisy
mbox 2 pres - low headroom. sounds ok with dynamic mics but lacks actual dynamics. noise ridden. bad for condensers or anything with a dynamic range. avoid at all costs.
i hope that this helps you make a choice. to sum it up:
the great river is the best pre ive ever used. the mackie would be best if you need 8 channels (which you said you dont). and the art mpa gold would prbably fit your bill the best. lots of features, relatively cheap, great sound once the tubes are changed (they come with crappy tubes)
digi 002 console, digi 003 rack, presonus digimax 96k, and a mackie onyx 800r, the brick, art mpa gold, art v3 tube mp, mbox 2
all pres tested with a u87, and audio technica 4047, an sm57, and a senn 421
results rundown:
1-great river - always sounded the best against the other pres. most depth, best low end response, never sounds fizzy or harsh. I wish i would have got one of these when i started recording. amazing on everything, especially bass and vocals. i wish i had a board with 24 of these things. very punchy. makes any mic you have sound 1000% better, 57s can be used on guitars again!
2- two way tie
onyx 800r/art mpa gold
onyx 800r - 8 channels, very clear, not over hyped, very versitile, good clean response that works well on drums and guitars. great dynamics and headroom
art mpa gold - 2 channels, upgraded cheap stock tubes(very easy) tons of variety in sound. great for getting nice tube clipping. has lots and lots of things to toy around with, mic impedance, plate voltage, tube saturation. sounds awesome awesome on snare drum, kick drum, vox(with high plate voltage), and clean guitars. all around great performer. easy to use
3 - groove tubes "the brick" - a little low on the gain side. upgraded the tubes. super awesome on bass and aggressive vocals. cool on acoustic guitar, crappy on a kick drum. implies a heavy "tube sound" on the signal(reduced extreme highs and lows, compressed mid range). very useful and relatively cheap.
5 - digi 003 rack internal pres/
digi 003 - decent overall pres, does not have the depth of of the mackie or great river but can be useful for things like toms or maybe guitars. not a bad pre but not spectacular. would always use the mackie before the digi 003
6 - presonus digimax - another decent pre. kind of harsh and fizzy but much better than a lot of stock board pres(mbox 2 and digi 002 im pointing at you). lacks a super clear low end but still very acceptable. sounds good better with dynamics than condensers, no go for ribbon mics. probably would not buy again and only use in a pinch.
7 - tie for last place
digi 002 - very flat(boring) sounding. no low end or punch. bad for vocals or anything that will be the focus of your mix. can be very harsh and nasally. dislike the most. good for demos. very noisy
mbox 2 pres - low headroom. sounds ok with dynamic mics but lacks actual dynamics. noise ridden. bad for condensers or anything with a dynamic range. avoid at all costs.
i hope that this helps you make a choice. to sum it up:
the great river is the best pre ive ever used. the mackie would be best if you need 8 channels (which you said you dont). and the art mpa gold would prbably fit your bill the best. lots of features, relatively cheap, great sound once the tubes are changed (they come with crappy tubes)