Using a good preamp with headphone amp worth it?

I have a small headphone setup for use when I can't use my main rig, but I'm finding that I'm using the headphone rig more and more. In this system I'm using a small passive preamp because I have more than one source and I also share it with a small self-powered sub/sat set. The preamp is fine, but it's not as good as going direct from source to headphone amp. The headphone amp is a good one -- the Grace 901 -- and my headphones are very good as well (Sennheiser HD600s and Audio technica W1000s). I also have a backup Stax set-up that I had packed up to sell, but put back just to be sure I want to do that. I run the headphone amp through the tape out on the passive. My passive has two pairs of outputs, but using the tape out avoids having two volume controls in the signal path.

Here's my question: In this case, would using a high-quality active (possibly tube) preamp be worth it? When using the tape out is the electronics of the preamp bypassed (especially with tubes)? In other words, is it not worth it to have a high-quality preamp if the source signal passes through the tape loop and into the headphone amp? If I were to use an output instead of the tape loop is having two volume controls in the signal path going to negate any added benefit of having a high-quality preamp (the Grace has a very high-quality volume control)?

The preamp currently serves primarily as a source selector, but it also serves as the volume control for the sub/sat system (which is of decent quality, but certainly not hi-fi). Someday, I may consider using a pair of small "bookshelf" speakers instead of the sub/sat (adding a power amp of course), but I think my wife will continue to prefer the diminutive apppearance of the sub/sat).

If you have any recomendations for preamps, here are my needs:
* at least 3 sources
* tape out
* preferably 2 outputs (to power amps)
* prefer diminutive appearance -- small and/or low height

The Sonic Frontiers Line 1, 2, 3 pre-amps all have the features you want AND a high quality heaphone output jack, and yes the headphone system is driven through the tubes. Also, the SF pre-amps use the electronic system designed by Headroom for their headphone system.

I have both a Line 1 and a Line 2SE and the headphone systems are excellent IMO, but then I'm not familiar w/ your Grace unit. I do use Sennheiser 600 headphones. However, the Line series pre-amps are full size, ie not diminutive at all. I can recommend any of these SF pre-amps for both headphone and regular pre-amp use. They're very versatile-- no longer in production, but available used. Cheers. Craig
What is your budget?

I am running my Creek OBH-11 through my passive ATC SCA-2. I run the amp through the tape loop as well. They are not full sized preamps and are relatively inexpensive for such a high quality preamp ... 1500 new.

But you can't really ever find them used.
I had a Headroom Maxed Out Home headphone amp. Since I used it for all headphone listining, I never used the headphone jack on my Cary SLP 2002 preamp. After about 18 months of using and tube rolling the Cary pre,one night, I just decided to try its tubed headphone output. The sound through my Senn600s was so much better comming from this output powered by the pre's NOS Bugle Boy 7316s that I put the Maxed Out Home for sale on Audiogon the next day.