kalali
I use a Schiit Sys, two inputs and volume control, all for $49. Very transparent.
+1 for this.
Simple test is, to go direct from source to amp, with a very quiet starting CD (eg:Ravels Bolero), with your finger on the stop button in case it gets too loud.
This is the most transparent transfer from source to amp you can possibly ever get.
Then get the closest to that with a passive pre in between.
Cheers George