Headphones vs studio monitors often don't translate well as most headphones are nowhere near flat and studio monitors are effected by their positioning and the room itself. Seems you have a decent amount of room fixes already in place so you should be covered for the studio monitors. Headphones will heavily depend on the model used. I suggest looking up your headphone model in the
AutoEQ correction database and applying the graphic EQ settings to the Output 1 graphic EQ to correct their response.
For headphones use the reverb block as room reverb to add a sense of space. Otherwise it can sound too direct. Leave it out when actually recording. Also use the headphone output on the FM3 over the Focusrite, the FM3's headphones amp is a lot better.
My setup is not all that different from yours. I use the Focusrite Scarlett 6i6 2nd gen into Genelec M040 monitors. I run the FM3 SPDIF out to the SPDIF In on the Focusrite. Since the 2i2 does not have this your sound will be to some degree effected by the mic preamps on it. That still should not be a big issue.
I don't think you will be any happier with a Quad Cortex. I've owned one and it can't really do anything (except captures) that the FM3 doesn't. If you struggle with the FM3's sound you will have the same issues on the QC.
Listening to your 3 sound comparison to me the 1st clip is fine, 2nd clip sounds odd and the 3rd one I could use just fine in a mix with some low cut applied. I think 1 and 3 would beef up nicely with drums and bass added. They definitely sound better when I turn up my headphones louder.