Tube Pre amp with tone control suggestions

The  Schiit Loki is an add on which costs $149. I have never heard it and am in no way associated with it. But It may be a less expensive alternative. Another alternative MAY be  a subwoofer. However that depends on your speakers . IE, my speakers have very good mids and highs but lack bass. Generally I set the subs and forget them. But every now and then I just need to tweak the lows or highs. Too much bass kills the highs. Too little bass takes away the punch. But again, my system is at a good place where it works for me. Not sure it is for everyone, especially if you are fighting too much bass as it is.

All excellent suggestions. I have several Subs I have put in and out. Don't really want to go to sub route. I have a good sub and it definitely does add to it
, I have various speakers that I can use cornwall's tannoy mg12 a few others. I know none of these speakers lack the bass when being put to them. I will look into that $149 option.

The Schiit Loki is an excellent EQ, but can only be used in a single-ended setup. It is the most transparent analogue EQ I've ever heard. 

Interesting. My amps are single ended, Audio Note P4 mono block's, but I am not sure about the pre amp

As a couple of others have already, I'll also throw in my recommendation for the Luxman CL-38. I bought the standard version a few years ago and liked it so much I bought the SE version. Both models sound beautiful in my systems, and are well within your price range on the used market. The great thing about Luxman's approach is you can select the shelf frequency for both high and low, and the boost/cut isn't 'out of control'; it's tastefully done. And when you don't need the tone control, simply hit the defeat switch and the circuit is removed, given clean straight-through line signal.