Just though I'd chime in here.  The Onyx 800 ad 400 outboard mic pres are getting
great reviews and they have A/D conversion.  A recording Mic pre is different
than a board mic pre.  The Mackie pres offer Mid Side deocoding which can be
interesting, though I'd thing you'd want to decode M/S in the mixdown stage. 
Something like the ATI 8MX2 has a much nicer sound than a mackie pre.  That being
said, focusrite has com out with a fairly inexpensive line of Mic pres with A/D.
 The TrakMaster Pro comes to mind.  For about $300 you get a nice pre and a
S/PDIF out.  Believe it or not, I really like my Presonus DIGITube.  Of course, I
have a bunch of 50's era 12AX7 tubes I got from my grandfater (a TV repair man
after the second war) which help it to sound really great.  It also has S/PDIF
out and an instert of you want to put a compressor or limiter in before the A/D.
 Of course the question you really have to ask is, do you want that color that
you get from a U/A.  If that's what you're after, then you'll need to get that
U/A.  (Or build it, if that kit stuff is as good as it seems on the website!)  I
recently recorded through an Earthworks and a Sennheiser 421.  The reason I know
is because my horn sounded so killing I asked the engineer what pre he was using.
 So I guess I'm saying, it's all what you are after.  The beautiful ting about
Ardour is that you don't get stuck with specific hardware, unlike some other
softwares out there.

Matthew Polashek
matt@tinysongs.com
www.tinysongs.com