Convenience. The idea is that with an HT bypass you never have to re-set the preamp volume to unity.
No matter how you were listening to music, once you switch to HT bypass the gain through the preamp is always the same.
Could you mark a spot on a conventional preamp, and use it all the time for L/R outputs of a 5.1 processor? Sure, but it's inconvenient. :)
Technically HT bypass does not have to be unity gain, it just has to be exactly the same gain every time it is switched to. The HT processor will handle any differences in the speaker configuration settings.
No matter how you were listening to music, once you switch to HT bypass the gain through the preamp is always the same.
Could you mark a spot on a conventional preamp, and use it all the time for L/R outputs of a 5.1 processor? Sure, but it's inconvenient. :)
Technically HT bypass does not have to be unity gain, it just has to be exactly the same gain every time it is switched to. The HT processor will handle any differences in the speaker configuration settings.