Soix is right on both counts.
A tube pre-amp with pass-through will be turned on during HT playback and will simply be using up tube life for no benefit. Depending on the pre-amp, the tubes might be relatively inexpensive and it might not matter to you, but you do need to consider that fact. Maybe some pre-amps turn off the active tube stage when the HT bypass is engaged, but I'm not aware of any that do this.
Also, as he states, you don't need an HT pass-though. Any unused line level input on any pre-amp will work. You simply need to set a reference level on the volume control before calibrating the HT setup and you need to set the volume control to that reference level whenever using the HT input.
However, the HT bypass switch is a nice option because it eliminates one step in turning-on your HT setup for each use.
Enjoy,
TIC
A tube pre-amp with pass-through will be turned on during HT playback and will simply be using up tube life for no benefit. Depending on the pre-amp, the tubes might be relatively inexpensive and it might not matter to you, but you do need to consider that fact. Maybe some pre-amps turn off the active tube stage when the HT bypass is engaged, but I'm not aware of any that do this.
Also, as he states, you don't need an HT pass-though. Any unused line level input on any pre-amp will work. You simply need to set a reference level on the volume control before calibrating the HT setup and you need to set the volume control to that reference level whenever using the HT input.
However, the HT bypass switch is a nice option because it eliminates one step in turning-on your HT setup for each use.
Enjoy,
TIC