Looking for an used, inexpensive pre amp

Any of the chip amps totally benefit by having a tube preamp in front of them to warm up the sound.

Having said that I might have a tube preamp for you under $100.  It is an Aric Audio preamp and has 3 line stage inputs.  Is that enough for you?  If not, I would add a switchbox as mentioned above.  My friend used this preamp with his Fleawatt chip amp and it solidly improved the Fleawatt's already great sound.  I think it may just need new tubes (2-12au7's).  Once I get new tubes, I'll test to make sure its working.  Price will be $50+cost of tubes.  By far, this is the best deal or sonic improvement you'll ever find for the price.

Downside, is that I'm very busy right now with lots of projects to get done this month.  If you are able to be patient, this would be a excellent deal for you.  Thanks,
Lou

Hi Will 
I have a Counterpoint SA2000 with upgrades. Listed on eBay

You can sometimes find Emotiva UMC-1 or UMC-2 pre/pros for 200-300.  They have some bugs but they sound great and accept many inputs.

Nad C160 is a fine preamp, I have the C162 and like it.  In 100-200 price range, you can probably get a decent vintage unit.  Look at Nikko or Yamaha preamps from the 80's.