The only problem I'd see with applying PLIIx to the 7.1 analog input is knowing whether or not the surround back inputs are active. Some people with HD-DVD players have used splitters and piped the surrounds to both surround and surround back inputs - it's not PLIIx, but it brings the rear surrounds into the mix.

I remember hearing something about the Toshiba's sub being a bit low - you should be able to bump the Toshiba's sub output trim up by whatever it's out of whack and be fine, assuming you know how far off it is.