It's looking pretty good, Mark. Better than I expected.
By the way, your "With desk left" measurement is all messed up: no use. something must have happened while that was running: maybe some sort of loud noise hit the room. so you should repeat that test, if you want to have a complete record.
However, you seem to have created some type of resonant "thing" with your desk, that is resonating at about 54 Hz: take a look at the waterfalls for the right speaker, with no desk, then with the desk:
And the same thing for "Both - no desk" and "both - with desk":
Something is ringing loud and long at 54 Hz. There's also some much quieter ringing at 78Hz and 163 Hz. I would suggest that you try to figure out what that is, and fix it.
The other issue (which was to be expected) is that you now have a slight dip around 1 kHz. That's typical with speakers placed on meter bridges, which is similar to what you are doing, basically, and is due to comb filtering from the desk surface. There's not much you can do about that, unfortunately, but it isn't all that big. Just be careful if you find yourself boosting 1k - 1.5k a lot in your mixes: it might not be necessary.
Hell yes! :) Well, to my way of thinking, anyway. Some don't agree with that, and say that subs are not a good idea, but when you have small mains in a small room, I think you need the extra extension that the sub will give you. To accompany your A7's, I'd suggest a Sub-10. - Stuart -2. Would a subwoofer be a good thing to acquire some time down the road, even in such a small room?