On the subject of the Behringer ADA-8000 and it being not worth "modding", that's not quite the final verdict.
They tend to fail in a common way, and in the end, I did come up with a solution, though it takes someone with some basic tech-ing/solder-slinging skills to make it all happen.
This is NOT designed to improve the sound in any way, it is intended to prevent the all-too-common power-transformer failure, which tends to give up after a year or two.
Details
here.
Looking on eBay, you'll find plenty of these things which "just wouldn't power up one day..."
Myself, I've used (and repaired) the ADA-8000, but I presently use the Rosetta. I have to say that I'm 100% in agreement with Clifford; while the Behringer gives you 8 inputs, 8 mic pres, phantom power and functions very well for about $185 street price, the Apogee is the one which sounds good!
And as for using external mic pres with the Behringer to improve the sound... don't bother. The Behringer just resistively pads down any line level signals and feeds it through the same Behringer mic preamp circuit, so there's no way to "bypass the damage"...
Keith