you have a couple of options:
consider to re-organize your tracks by some intermediate submixing, to get along with 24 ch.
Look for an expansion chassis with Expresscard connection plus (at least) 2 TDM cards to get a reasonable amount of processing resources plus 1 io-interface (882/888 etc).
(the TDM software won't run without the hardware io-box)
Get a G4 tower with the same amount of cards and the io-interface.
The latter is the most easy way because there are plenty of G4 Macs, TDM cards and interfaces, all for very affordable prices. Sometimes even complete systems.
If you like the handling of PT, then a TDM system is worth considering anyway.
It saves your Mac a significant amount of CPU cycles and the processing on the Motorola DSPs is excellent.
(myself using a G3 450Mhz B/W with relatively few plugins - I cherry-picked for a couple of months from what was available and imh ears the TDM kind of soundcolor is much more pleasing than the one from most current Windoze systems)