Hi Dave.
I was playing with C6 & a few midi files last night, and the option to use HalSonicSe in multitimbral mode works really well.
Of course, HalSonicSe will also automatically set up all the right sounds for you too (so long as the GM file cotains that info) - and volume, pan & effects too (HalSe switches to GM mode).
There’s no way (that I know of) of using any other plugin (automatically) instead.
You could, however, choose the above option, then just replace the instance of HalSonicSe that appears in the instrument rack with Bandstand - and finally re-route the midi track outputs.
(might save you a bit of setting up time …)