Please explain preamp theater pass thru

In wanting to upgrade my system as a move toward more music and less HT, I have recently purchased Vandersteen 3a Signatures. I currently have a Classe SSP25 surround processor. I would like to add a tubed preamp for music.

After researching on the gon, it appears that a nice preamp with a processor loop, or theater pass thru as I've also heard it called, would benefit me in this upgrade. My understanding is that in bypass mode, the preamp becomes no more than a wire allowing the pre/pro to send its digital signal out without the preamp coming into play. Unfortunately, I have become confused on this issue as several people are telling me that any preamp will suffice by just connecting to any source mode of the preamp but having to make some adjustments to the gain since the pre/pro cannot control the volume gain in this configuration. Just doesn't sound right to me. Again, my understanding is that you want the preamp out of the signal path so that the pre/pro can do its thing. Occurs to me without a pass thru, the 2 channel preamp would send out its own signal to the mains even in HT mode instead of allowing the pre/pro signal to send its info to the speakers.

Ouch, my head hurts. Can someone (who really knows) please clarify this for me.

Mucha Gracias to anyone that can help...

P.S. I have another thread under the amps/preamps discussion section asking about recommendations on a good preamp for my system. Any suggestions on a good preamp would also be appreciated.
You had the right idea in the first place. The HT passthrough does just that. It passes the signal from the pre-pro directly on to the power, bypassing the preamp's own circuits. This allows the pre-pro to control the overall volume of everything, including the main left and right speakers. When you switch the preamp's selector over to another source, the preamp takes back over the main left and right channels. Of course, you'll want to mute or turn off the pre-pro when you switch the preamp to another source. Hope this helps.

As for a recommendation for a good preamp, I'm kind of partial to Audio Research myself. But there a lot of good ones out there. Good luck.
Dwud- Whether the pre-amp is in or "out of the signal path" as you've mentioned, isn't really a make or break issue. If the analog pre-amp is a good unit, it won't be hurting(?) the processed signal from your surround unit. As others have suggested, simply select the appropriate input on the analog pre-amp, and place the volume control at an easily repeatable location (9:00, or 10:00, or ?? position) and then perform the processor channel volume setup routine to balance out speaker levels. Everytime you want to listen to HT, select the correct input on the analog pre-amp and place the volume control in the same location. Now you can use the remote for the processor just like the pre-amp wasn't there. Given the potential improvement in 2 channel listening with a good analog pre-amp, and considering that most analog pre-amps don't have a "pass-thru" feature, this will greatly increase the number of analog pre-amps for your consideration. You may actually find that you prefer the sound of the HT running through a good analog pre-amp. Enjoy.
Excellent explainations. I now fully understand and can get on with my search for a nice preamp without the limitation of needing a processor loop on the pre.

Many thanks...
The HT bypass option does make things a little easier to use. I for instance have the Cary SLP2002 which has the HT bypass option with both balanced and single ended inputs. When this preamp is flipped to HT bypass then you do not even need the Cary powered up for the HT setup to work because it is simply bypassing all of the Cary's "2 -Channel" functions with a wire connected from the HT input to the main outputs. If you go with a preamp that doesn't have a HT bypass then look for one that will allow you to preset the gain on a specific input. That way when you select that input which you have your HT setup coming into, you do not have to worry about recalibrating the volume or trying to get it right everytime. The BAT preamps have this function and would work nicely.