yep, if you don’t need to externally sync with anything you can manage fine without a Sync I/O. Obviously you’ll need an interface too – I didn’t mention that. A 192 I/O, 192 Dig, 96 I/0, or one of the devices that uses the digilink interface (apogee etc…)
Waves can be run natively under RTAS for almost but not all of their plugs – you’d have to see on their website which ones have to be run TDM. You could start with just the HD1 system and see how things go using a combo of both TDM processing on the HD cards and RTAS on the mac pro, then if you need some more power further down the line you could pick up an APA-32 at that stage.