The BR600 records only to 2 simultaneous tracks (it can playback 8 but record only 2 at a time). The 192 records to 2 tracks but can have an unlimited number of tracks depending on your DAW software and pc (remember, however, the PT M-Powered is limited to 48 audio tracks max).
The BR is limited to the size of the CF card included with it. The 192 will utilize whatever hard disk space you have (it's best to have at least 2 drives in a DAW.) In stock config, the BR600 comes with a 128 Mb CF card. A minute of mono wav recording at 44.1/16 comes to around 5 Mb of space; 8 tracks will take up 40 megs so that means 128 Mb CF card will only hold 3 mins of an 8 track recording (or roughly 24 track minutes at 44.1/16). The BR600 brochure shows the you can fit up to 65 total track minutes at MT2 settings. That means the BR is always set to use Roland's RDAC data compression algorithm (something similar to mp3 compression) - successive bounces within the unit will mean degraded audio quality.