Preamp with tone control.

Cool...and if you don't like it you can blame me. Weird thing...when listening to an ipod pluged into the "aux" input, I noticed sound bleeding into other inputs (like the CD input if I wasn't yet playing a CD and the pod was on). I assumed there was some design flaw in the preamp as I also assumed the ipod cable was OK. WRONG. I bought a Squeezebox Touch and some new Audioquest interconnects for it and the issue was solved...must have been crappy shielding on the other cables. Lesson learned.

mcintosh and carver have preamps with tone controls.

Also, some of the Van Alstine preamps have bass/treble controls which are defeatable. Used they could be within your price range. Of course, there's always an old Dynaco preamp, which can be had cheaply and fully restored here on Audiogon fairly often.

The Adcom 715 is great for the money...it just is.

Audio by Van Alstine preamps have very transparent tone controls. Their affect is subtle but very useful.