Preamp Help

This is over your budget but is clearly a level above the Schiit. 

Nice piece, just a little over my budget 

This Chase RLC-1 Remote Line Controller can do exactly what you want. You must have a remote, no controls on the unit

Use it with your existing preamp, and then ANY simple tube preamp, new or vintage with no remote controls, no special features on the preamp, just preferred sound.

I just sold one of my spares to an audiophile friend after he determined, like me and my friends, you cannot detect if it is in or out, it’s 120db S/N is true.

4 inputs, remote: input; volume; balance; mute; treble; bass

It has two pairs of outputs, (front, rear) identical, from the early era of quad, simply 4 speakers, no processing, so you can use 'rear'  for your sub, for a self-powered sub with it’s own crossover.

remote has a fader controlling the two identical outputs (front, rear)., so you could remotely adjust the sub’s volume relative to the main output.

I use one for all it’s features, one for remote power only, and:

I am using one downstairs in the garage/shop system’s receiver’s processor loop, gives me remote power, volume, mute, everything else goes into the preamp normally. That puts the RLC-1 in control only when using the processor loop.

Check out Vincent SA 32 ... Personally, I'd save my pennies and get one from Klaus at Odyssey Audio.  

I know you said you wanted tube but I know of nothing with that much flexibility.

How about the Parasound P7?  Really great remote with tone controls and bass management built in.  I would not recommend the 5.