PS Audio BHK lacking..

It should be better than a Rotel, I had the 250 for about 2 days and returned it.  In all fairness, I did purchase it used from The Music Room.  No problems returning.  It just is underpowered.  I had sold an old Adcom 555ii which would beat it hands down, no tubes too, and sounded sweeter.  I like PS Audio's marketing and return policy and the people - but the stuff is not high end in my opinion - right in there with MAC and Rotel.

@plaw - was that the BHK250? I don't have any comment in regards to their power, efficiency of your speakers, size of your room or the listening levels you enjoy..

I do know that a BHK250 does sound markedly better with the BHK Pre, honestly I can't speak as to why it's the case. But it is just so.

Contact PS Audio and explain your situation. They have some pretty decent tech people that can make the right suggestions. 
Even though they are "factory direct" now they have a good team of engineers. 

cdamiller-far from the truth

Next is what should I expect to pay. There is a set of Telefunken 12au7 on line, new for $400.

That’s high for experimenting. If you were sure that Telefunken was your favorite tube and that was a superb pair, maybe. You should be able to buy some nice tubes from a reputable dealer for $200 or less.

Here are a few good dealers. You can google them.

Andy Bouwman at Vintage Tube Services (he can be slow but many people swear by him)

Brent Jessee

Kevin Deal at Upscale Audio (some people find his personality abrasive)

Jim McShane

I hope others will chime in with those I’ve forgotten.

They will all talk to you about what tubes might work for you and they are probably all familiar with your pre.  I’ve read that Brent Jessee allows returns if you don’t like the tubes. Check that with him before buying.

Take your time shopping for tubes and listen to the stock tubes for a while to get familiar with the baseline sound of your pre. Then decide what you might like to change with new tubes.

There are good sellers on ebay, but it’s not where I would start my tube journey, especially if you don’t have a tube tester.