And to be clear, the AG500 of course sounds good, but it is more 'fat' in the low end than particularly tubey or warm in an absolute sense to my ear. I like to be able to get a burpy thump out of a rig easily, and I found that was one of the AG500's weaknesses (the mid voicing and EQ just didn't sit well with many cabs and especially J type basses to my ear). The RH will REALLY burp and 'chest thump' if you want it to, and it will get a bit bloomy and big like the AG if you really want it to.
The AG500 really has its own sound to me which many really dig, but you can get into trouble if you try to push it too much away from that tone by turning the knobs. The RH450 is more chamelion like, and can go a lot of different directions. However, it always stays more 'warm' than, for example, the Markbass heads or the much brighter Genz stuff IMO.
Don't forget about the MB LMII/III also. I can get it to do almost everything the RH450 does (using the VLE filter) other than full 'tube emulation' and grind, for much less money.
I'm again only talking about the head. I've never heard the cabs, but have no GAS to even try those.