That’s a good question!
Few headphones can compare with the big plush Beyerdynamic cushions. The Custom One Pro is still among the most comfortable headphones I’ve ever worn, and I think its ear pads are even more comfy than the DT880 pads…as long as you don’t mind the slightly sweaty leatherette.
The HRM5 and 6 both have a touch less roominess to their headbands and pads, but they’re also exceptionally comfy. Without knowing your personal headshape/tastes I can’t say which will be more comfortable for you, but I’d pick the Custom One Pro out of that selection, by a few hairs.
Sound quality is a toss-up. The Pioneer models are going to sound a little more like the 7506 and the M40X that you’ve enjoyed in the past. The Beyer has a slightly more laid back sound, and it can bring plenty of bass if you crank up the sliders. The Custom One Pro completely removes the harsh treble that Beyer is usually known for, and it’s their most friendly headphone as a result. At least, out of the several I’ve used.
From everything you’ve said, I’d lean towards the Beyers, but you won’t really know until you try one for yourself! Hope that helped you out a little. :)