I'm both confused and intrigued by this post. My wife and I both use the Avanti Quartos and we both wear 5mm boots. Neither of us have any problems with the fins and boots not working together. We both use elastic straps and each of use have a snug, but not tight, fit. So I don't know what your issue is that the boots don't work with those fins. Could you elaborate a bit more as what the issue is there?
And while we both use the Henderson Thermaxx wetsuit, ours are 3mm. We were our wetsuit legs over the boots and neither have had issues with the legs stretching.That could be a difference between the 3mm and the 5mm, but I'd be surprised.
I'm very curious as to what is causing this problem for you.
I have size 7 women's feet. With 3mm tropical short booties, the size small Quattros are too big. So I bought 6.5mm zip up boots with thicker soles and just overall thicker. This worked on land. Once I got in the water, this combination was wobbly, indicating it was a tad too loose. @uncfnp has suggested an even thicker soled boot than the one I have and it works for her, and I believe she is the same size feet as me. The Quattros doesn't come in an extra small. It's just a sizing issue really.
My Henderson Thermaxx legs stretched over my 6.5mm booties over 9 dives and they did not bounce back. I can no longer wear this wetsuit without these or another pair of thick boots.
I didn't expect them not to bounce back. I am bummed about it.