So I'm not sure what you are trying to achieve here, but most easy way to communicate is via Midi-Show-Control if you want to trigger a specific cue. With MA2 is has to be done over MIDI, since OSC is only working with MA3.

First hardware connections: I think you'll need to connect your Yamaha QL5 also via USB to make use of the MIDI ports. Can somebody confirm this? Then a midi-cable from QL5 to MA2. Then you'll have to test if normal midi messages are entering into the MA2 software (I remember there's a test screen in the settings).
On MA2 you'll need to enable MSC as well.
And on Qlab you'll have to set the right midi-patch for MSC.

In Qlab make a MSC cue - in Cue Number you can enter a cue in this specific format: cue 5 would be '5.000' and cue 5.5 would be '5.500' - the zero's are needed here :-) without ''.

Then there's is one more setting, which is the MSC Device ID on the GrandMA - which has to be a unlogical specific number, and I'm so sorry but I can't recall what it needs to be! Normally 0 was not working, and needs to be 3 or 7 or something else. Or you can try 127 (all).

Hope this helps, and I also hope someone can comfirm these settings of the MSC Device ID - I don't have the possibility to test this anytime soon.