I remember this thread!
The AMP is still going strong, as is the HD500x (might have played with settings and the like over the years, but it still sounds great). Plug the HD into the Effects Return, and bypass the amp's pre-amp.
Do not regret going for a bog standard bass combo in any way over an FRFR, as I know it definitely can handle the bass frequencies, and has more than enough power for any rehearsal / gig situation (it's been gigged a number of times).