We need to spearate 'inputs' from 'channels'.
Inputs are the number of sources you can connect to your system - ie. cd player, dvd, phono stage, etc....
Channels are the number of - well - channels you can control the volume of - ie. Front left, Front right, Center, Sub, etc....
The standard TAP unit has '1 or 6 INPUTS' and '2 CHANNELS'. For a typical music system or for systems combining music and an HT processor (as described below) this is just fine.
1- The TAP can be expanded to as many channels as you'd like by adding additional 2 channel expansion units. Each exapansion unit can have 1 or 6 inputs. For expansion channels you could use TVC based units for all channels but the less expensive units make more sense for surround channels - an all TVC 6 channel system would really add up cost wise!
2- The HT Bypass feature is a convienience to allow you to program any input connected to an HT processor / pre-amp to 'lock' it's volume when that input is selected. Usually this input volume would lock at unity gain but the volume can be set so it jumps and locks to any level. There is a small push button on the back that you press to toggle between normal and HT mode for each input - setting to HT programs it to jump to the volume it was on when the button is pressed. You know if an iput is in HT mode - it's led indicator turns red in HT mode rather than green (for normal mode). The way it works is the volume jumps to the programmed volume level as the HT input is selected and then the volume returns to the prev volume setting (likely much lower) when a new input is selected. It saves you from manually turning the TAP to a particular level each time you use that input and more importanly from remembering to turn the volume down after it is switched to a 'normal' input.
The two questions you had point to 2 alternate ways of setting up an HT in a TAP system so I'll expand on that a bit for clarity.
1- If you will use the TAP in a high quality system with decent speakers all around and intend on using SACD surround or DVD-A suround as a source then going with a 6 channel TAP system might make sense. Then you'd likely use the built in processing in your player and have no 'HT processor' in the system.
2- If you just need to patch an HT into your 2 channel system for use for movies, etc then very likely the best setup will be to add an HT processor (or a reciever with preamp outputs) to the system. Then for 2 channel music you have a really clean high quality signal path for music listenning and when you want to watch a movie in the system you:
1- Turn on the HT reciever (or processor)
2- Select the TAP input that the processor is connected to - that TAP input will jump to unity gain and stay there.
3- Now during the movie you simply use the processor to adjust the volume in the system - all channels stay level matched.
4- As you select a new input on the TAP the volume returns to the level it was at before jumping into HT bypass mode.
Hope that is the info you needed!