I have a SB 1.5 with the empty sockets.... I seem to recall the very first SB Pro - the 2x FM rather than OPL-3 - had Gameblaster option, too!
Which card might allow you to "have it all"?
I don't think thats possible. The Game Blaster chips on the Sound Blaster used the same I/O ports as the dual OPL2 chips of the Sound Blaster Pro. Maybe you are thinking of the Sound Blaster 2.0, which was based on the Pro 1.0 and worked similarly to it, even if it only had one OPL2 chip.
