You may have already solved this so congratulation because I've also looked around a lot(!) for a similar solution. I'm using the trio+ and firehawk fx as follows:
guitar --> trio guitar in --> trio fx send --> firehawk guitar in --> firehawk left 1/4" --> trio fx return
then
trio amp out -> mixer channel (x) in
trio mixer out -> mixer channel (y) in
mixer out left/right -> powered monitors 1/2
Yes the trio needs the guitar directly connected to the guitar input so it has a clean signal from which to do its magic, ie create bass and drum parts. The trio+ does not need the amp output to be connected to an amp. Connecting to an amp will color the sound of the firehawk's amp/cab models in a way I don't want. Going from the trio+ amp output to a (good) mixer and then out to speakers mitigates this issue. I use a Mackie 802 VLZ4. It is very clean as far as sound coloration (IMHO).
I know a mixer isn't in your set-up but if you can swing it, Mackie makes the 4-channel 402 VLZ4, which is only $99. There are plenty of others but I love my Mackie!
happy trails.
