Firstly, yes, the BC2 connected to the SY77 can be used to control a Breath Controlled sound in whatever you connect via MIDI (whether or not the connected device itself has a BC Input).

The best sax sound ever from a synthesizer would be heard from one of Yamaha's VL instruments. If you can find a used VL70-m, you will scare people with the realistic saxophone sounds from that unit, especially when addressing it with Breath Control. This little half rack module (discontinued) worth its weight in gold can deliver realistic horn sounds. There are also VL7, VL1 keyboards, and VL1m Rack modules but you will not find many of these on the used market as they are rarely if ever released from the original owners (they are one of those keeper products that evoke the "never, they'll have to pry it from my cold dead hands" response when asked about selling it. 🙂

Another alternate to that would be the MU100R which has the PLG100-VL card in it, basically a VL70M on a card. The MU100R has the MIDI in/out connections you're looking for too. I've got a similar setup and it sounds fantastic! The MU100R's are available for much less than the VL70M's which are rare and hard to find. Make sure you get the 'R' version, the simpler unit doesn't have the VL card in it. Also, make sure the VL and VH cards are still in it, sometimes sharks will take them out and sell them separately.

Thanks for the replies. Very helpful. I will do more research when I get home from work, but what would be the advantage of the VL70M over the MU100R? Looking fwd to picking up one of either of these instruments.

The VL70M is probably easier to make settings changes on, since it's a dedicated VL controller made for the BC units. It also has the Breath Control input jack on the unit where the MU100R does not.