If you wanted to actually hear the B4 coming through your keyboard and then to your sound system, it can be done Mike. Simply route your soundcard's audio output to the audio inputs of your board. I strongly recommend setting a very low level for both the signal / audio coming out of the soundcard and using a low input setting and adjusting from there ( the Tyros has adjustable inputs I would think ).

I used to do this when I first started using soundfonts. I would use the PA80 as the midi controller, and then send the soundfont's audio ( soundcard to be exact output ) back into the PA80 so that I could process it with the PA80's internal effects and / or layer the soundfont's output with an internal PA80 voice. I was able to make some very cool synth sounds this way, and also was able to supplement what I thoguht was a somewahat weak PA80 ac piano voice.

I no longer do that as my current soundcard is actually the driver for my entire soundsystem. Via a mixer, my internal ( soft ) instruments and my hardware are processed through it before it gets routed to my studio's sound system.

One other cool trick I've used was to send the PA80's internal guitar sounds out and then back into the PA80 so that I could use the guitar effects from the plug in vocal harmony / guitar board. I set the PA80 up so the internal voices would not play through the speakers or the main outputs ( 1 and 2 ). I then sent the guitar sound out through outputs 3 and 4, and rerouted them back into the board via the line inputs. As I mentioned, I set the board up so that internal voices would not play through the main outputs ( 1 and 2 ), but so that the audio coming from the line inputs would. it worked nicely.

AJ