Pete....
I ran the RM4 in through the Series FX return of the RM50HB, to me it made the high end response sound different when compared with the module in the RM50HB directly....this could have been a matter of needing to balance the RM4 Master and Module FX Levels differently or simply due to running through another tube/gain stage.
I vastly prefer the power section of the RM50HB compared with the RM100
Would have loveed to try the RM4 / RT2/50 combo...there was an RT2 on eBay recently but I decided to sell the RM4 already
I emailed you tracking info by the way.
...Steve