So far I haven't had any problems at all running a few of these at a time in Pro Tools. I am running the Waves Ltd. API 2500 Stereo Compressor on a Pro Tools HD system and it has run very smoothly in the short time that I have been using this plug-in. I've been able to run three or four at once, but I can't speak to how well it would run after that although I don't think it would be too much of a problem. I've only been using the Waves Ltd. API 2500 Stereo Compressor for a few months as this is a fairly new plug-in on the market.
In the few months that I have been using the Waves Ltd. API 2500 Stereo Compressor I have grown to really enjoy using this powerful piece of software. I have used it for compressing guitars and vocals mostly thus far, but it is definitely versatile enough where you could use it on just about anything that you would want to use compression on. The price of the Waves Ltd. API 2500 Stereo Compressor isn't all that cheap, but is priced reasonably considering that it is a Waves plug-in on considerable power. The sound quality is great and while it doesn't sound exactly like the original hardware API 2500, it does sound quite good and surprisingly warm for a plug-in. I would highly recommend checking out the Waves Ltd. API 2500 Stereo Compressor and all of the new Waves API emulation plug-ins.