Like you said earlier, a preamp with separate outs would work, which is what a mixer does, giving you preamps and line level signals to feed the Delta 1010lt. A mixer with the ability to have separate outputs for each input is what you need. Some mixers have the ability to send a direct out from the channel. Some mixers make you use the effects sends to send a copy out; you'd want one with four of those if you want to record four mics. Some mixers have submix outputs in addition to the effect sends, which is what I happen to use. You could even get 4 separate mic preamps if you wanted.

Or go with the FastTrack..convenient for sure, but USB throughput is the only question there. I am interested in the fasttrack myself for my new machines.

I do not work here, but the benefits are still awesome
Make your sound your own!