Having tube amplification for HT is possible although you will need an SS processor since i still have to hear about a tube based processor. The best way to go about this is to use monoblocks each of them powering each speaker. You can also use 2 channel tube amplifiers but then you might want to go 6.1 so that you wont waste a channel of amplification. Using the same amplification would also ensure that you have a timbre across the different channels since timbre seems to be key to a good HT system.
I might be wrong but HT/movies might require fasting sounding equipment while tube sound is mostly slower and more relaxed. Thats just logic but then again i cold be wrong hehehe. Havent tried a tube powered HT yet.
my 2 cents worth