Advice on an equipment purchase

Very good advice there, also you mention you alrdy have some sort of mixer, maybe it has direct outs of some sort, so you can get a soundcard without pres.

Do you have any acoustic treatment in this basement? If not it could be time and money well spent to look into it. Especially if your recordings tend to be boomy and muddy. Homebuilt basstraps are cheap, easy to build and makes a world of difference. Good luck with the recording!

Really good advice from volt on all counts. SM57s are great mics, but buying some similarly-priced small and large diapragm condensers will give you more choices and flexibility. Buying mics in pairs is always good practice. And room treatment will make a big, big difference. How's your monitoring situation?