Looking for a tube preamp with remote control.

Why not just get an add on passive remote control and insert it into your pre-amps tape loop? Worked well for me.  A good quality one will not change the sound of your system.

Newbee,

Sounds like a great idea.
 Is it hard to set up?

I like the idea of a passive remote volume control add-on.  The best, to me, are transformer-based volume controllers because they don't degrade dynamics (liveliness) as much as other forms of passive volume controls.  I like the Myemia control because it has a lot of steps to the attenuator (with few steps the "right" volume always seems to be between two steps), and it also allows for remote balance setting.  It is a little out of your price range, but, it is worth it.

http://www.myemia.com/Remote.html

Simple set up. Two additional short I/C's to and from tape out/in and plug it in. When you want to use it you just switch to 'tape in'. If you want to hear it without the remote you simply switch back to 'source'. FWIW I used a Placette which is a high quality one at a moderate price. When you can find one used it sells for about $600 +/-. There are different models but the one you would want is a single source unit. (They also make a unit which allows 3 sources and they have an active unit as well (very expensive).