Well, my impression during install was that those options enabled FFX-4 to operate within those environments, rather than host those formats. I can't find anything in the interface that indicates it hosts or chains VST, but I haven't been using it too much longer than you have, so I might just nominate YOU as the new Resident Expert.
As for cool plugins, I'm only doing playback so there isn't much I need. I found a great little EQ module called "Linear Phase Graphic EQ 2", or LPGEQ2. It is written by some guys called "Slim Slow Slider." The thing was well reviewed, didn't contain any obvious spyware that I could find, and most importantly, FREE. You can find this and other great plugins at
www.kvraudio.com.
I use the LPGEQ 2 module for Global and/or Room EQ, and I use a standard-format plugin from scthom, available on jriver third-party plugin board, called "EQdb". This allows me to make track-based or selected-group based EQ changes in the DSP studio, which EQdb calls and implements on playback. It is a brilliant idea, although highly specialized, and there is a design kink: since MC queues up tracks 5 seconds in advance, EQ changes are made for the upcoming track during the fadeout of the current track. If you have huge EQ changes between tracks, this will be noticable. I highly recommend it; in my experience replay gain doesn't give complete results in about 10% of the cases, and you can use this plugin to fine-tune that. If you try it, it's a standard-format plugin that installs in the usual way.
Also look at the Ozone 3 plugin from Izotope, that hammer mentions. You can get a free 10-day trial, but it then bugs out unless you fork over $250. It doesn't do anything for the audiophile than free plugins don't, but it is so incredibly cool looking that 10 days spent staring at it seem like 10 days well spent.