The main reason for HT pass thru is to hook up an HT receiver and a preamp to the same main front amp & speakers w/o any unhooking or wire swapping. When you watch a movie, the receivers L/R preamp outs get routed thru the preamp, untouched by tone controls or volume knob. But by switching inputs, the reciever is totally out of the system for music. Very slick.
With my set up I don't have any wire swapping or tone controls, only the volume knob and since the S/N on the Preamp is 115db and the THD is .002% I can run it at 2:00 and no noise whatsoever. (even with your ear to the speaker)
I lucked out years ago and got the straight wire with gain cliche.
Then for Music the CDP analog and TT analog go straight into the Preamp>Power AMP>Speakers. That signal never heard of a HT receiver.
Then heaven help you if you switch inputs and forget to turn it down!
I set the preamp at 2:00, which is two hours higher than I could ever listen to it (highest is 12:00) during normal 2 channel analog music listening, and then run the HT channel setup test tones, and set the levels. The fronts are then adjusted so I don't have to worry about over driving.
Out of curiosity, I just went out and checked and with the receiver on and switched in, but with the recievers volume control turned down so it produces no audible signal, I can turn my preamp gain to max (till it stops turning) and not a sound out of the speakers (ear to speaker again)
No hiss, no hash, nada...

That makes me a happy camper
And to think I almost sold this preamp for peanuts (in fact I almost gave it to the Salvation Army with a pair of Maggies a couple years ago.
Only "slight" inconvenience is when I switch to HT, I have to "turn up" the gain on the Preamp, but I do that when I put the DVD in.
I haven't noticed any sonic problems on films, but I guess the by-pass might take a "part, or in some cases two or three", out of the chain, and that is always good. Or at least is seldom hurts
Regards,
John Casler
VMPS LA CA USA
SUMMIT Audio Video
310-446-0138
800-320-6884 (order desk)
[email protected]http://www.audiocircle.com/index.php?action=systems;system=72http://my.register.com/summitaudiovideo.com/index.html