Just FYI, I sent GAIN an inquiry regarding the use of MT4, and
this was the reply :

"If you use Trading Station with FXCM, you will need to apply for a MetaTrader 4 account with us as the Trading Station accounts will be moved to our ForexTrader Pro platform. If you use MetaTrader 4 with FXCM, the account will be moved to our MetaTrader 4. "

I assume that accounts accessed through FxConnect (which I think non-MT4 Zorro uses) would be moved to the ForexTrader Pro platform, so we would need to open an MT4 account with GAIN.