I don't know if it really helps but I have a POD HD400 that I use in conjunction with my Catalyst, but I don't use any of the amp models in the POD. I've turned my HD400 into a virtual pedalboard by pressing the FX ONLY button and then run it into the front-end of the Catalyst. I like the amp sounds that the Cat provides, and I use its reverb effects as well. I then let the HD400 provide delays, tremolos, modulation effects. I also have my own real gain pedals in the effects loop of the POD and use that when I want Zen drive, OCD, etc sounds, so I'm not really using the gain models built into the POD.
I've seen videos talking about how great the M9 was back in the day and essentially that's what is available inside your HD500X.