I've heard some nice things about those Onyx mixers actually. Might be your best bang for buck ratio there...
I had a Presonus Digimax. not bad. you can get them for cheaper than $800 if you look hard enough...

must you have the ADAT out? if not, look into a True Precision 8. might be out of range, but a killer 8 channel pre...

unless youre going into an 002 or something to get more in. the presonus or Onyx will suit you well. Id go the Onyx tho. Probably as nice if not nicer pres than the digimax, and you get a digital mixer as well.

if you want some real nice pres check out the SCAs. They have several styles of pres. If you cant afford 8 at a time just get what you can afford and then add more later. I wish I went this route. But I have nothing bad to say about the mackie 800r that I own.

sort of on topic....
suppose one picks the 800r, but not necessarily because its a preamp,. but to add 8 channels quick and dirty, because one doesnt trust the alesis ai3 for whatever reason.
Are there any drawbacks to using a preamp stage for an expansion. IE to just run anything through with no gain most of the time?

I'll second the SCA preamps. The initial invest for the PSU and case bumps up the price, but where else can you get "real" preamps for under $400 per channel? You can't.

http://www.seventhcircleaudio.com

If you want really, really high quality preamps pay 1000/2000 dollars per channel but you state budget so...

These days nobody makes bad preamps anymore in your price range, even Behringer does a decent job. They all work fine for the job they are supposed to do: power your mics. Do not expect anything more, so no amazing character, unbelievable loudness etc. But if you have some good mics, good recording skills and good ears you can make some kick ass recordings with all of them! I'd go for the Focusrite by the way, don't ask me why, I just like it.

I'm trying to prevent him from getting something he'll end up dumping in 1 year. It's mistake i've made. We settle on something cheaper just for more channels. But other than drums you hards ever need more than 3 or 4 pres at a time.

i record blues and jazz musicians live of the floor and find myself using up to 6 channels sometimes just for two musicians. it really all depends on what is going on at the time.

Perhaps this one:

http://www.jlmaudio.com/TMP8.htm

Audient ASP008 for me, although the ADAT board is limited to 48 kHz.