not Syn 1 but with RM22/RM4 use a Weber Mass. works well with no real loss of tone, you have presence to make u for it + it has treble compensation build it at 3 settings.
I used it with an Rm50 and RT2/50 in the past with very good results. They can be found fairly cheap on Reverb/Ebay.
I have a THD Hotplate but never really needed it with the excellent MV on the RM50...there's also the option of running direct into a sound card and using an IR through monitors these days.
I just picked up one these Jet City ISO cabinets. It works really well to keep levels down. I also throw blankets over it when recording. You can use 2 mics in it and drop different speakers in it. I'm pretty happy with it. They're only $200.
