I had a similar problem.  I work at 88.2 and, as you said, the MX only works at 48Khz max.  So, I picked up a pair of B'ringer Ultramatch Pros (DIG 1 and DIG 2) for halving the sample rate.  Since these units are not AD/DA converters or preamps, or anything else that I would be nervous about, they work perfectly.  Everything stays in the digital realm, and I use the DM's clock to slave them. I send my DIG 1 out at 88.2, down convert to 44.1 in the Ultramatch, to trigger the verbs in the MX, then return back to the board to up-convert back to 88.2.  Now don't get your panties in a knot, I only do this for triggering the effects.  For instance, everything in my mix stays at 88.2, but I might take a copy of my vocal track or guitar track and send it out to the MX or other digital effects (like a TC Helicon Voice Works) to jiggle the Delays or verbs in the MX, and then bring that back to two tracks in Reaper, to be mixed in.  They sound fantastic and I don't have to take up two channels of analog outs or have to DA/AD convert.  Just my way of doing it.  Again, very happy with the results.