First thing to realize is Protools isn't just software on it's own like Cubase, Logic etc ... it's a combination of specific cards and interfaces, the software it's self AND a certified PC or Mac .... so a Protools system is all those three things. The first two are compulsory, the latter is recommended.
To get the same PT system they use in professional studios you need at least one HD card, one 192 interface and one Mac or certified PC. That will set you back about 7K but you do get the software for nothing This is called Protools HD, meaning Hi Def cos it supports upto 196Khz sampling rate rather than the older 44 or 48Khz of the older PT system. This is a DSP based system meaning the Protools card or cards do all the work while the PC or Mac just runs the operating system. There's no latency and the recording quality is superb.
Most home users use Protools LE, a slightly crippled version of the real thing. Using the best LE interface still only lets you use upto 18 channels of in \ out and 48 audio tracks. Theres no plugin latency compensation and the system has none of it's own DSP, so your computer has to do all the work. Popular interfaces are the Digi 001, 002, 003 and Mboxs. Recording quality is fine but no better than the competition at a similar price.
Protools M powered is an even more crippled version of PT that runs on Maudio hardware. This is for the budget market but still fine for learning the standard PT shortcuts and work flow.
So you can buy the software but you still need certain hardware. Either HD, LE or Maudio hardware. The only version of Protools that ran on anything was Protools Free, but that only supported 8 tracks and only ran on Win98 so now defunct
If your using a computer to record music then Protools is the best bet IMO. If your using a computer to MAKE music then almost anything else is better IMO
But then the summing issues drive me mental. If it just sorted those out I probably wouldnt be trying to move over to reaper.
What's wrong with the summing? Sounds fine to me and I find it hard to believe that the developers of a £60 DAW package have managed to outdo a company like Steinberg on such a critical issue. I could be wrong but I'm curious to know what the issue is.