Meridian Digital Speakers with Normal Preamp

If you have a 5.1 premp, I am certain you can select from it's menu to make the digital output a two channel stereo compatible output. I (guessing) think? that the ouput would have to be in a compatible form for your speakers digital input. That is like not Dolby something or some other video codex. (I only know my Plasma TV will, digital out, work with my receiver, but NOT my two channel DAC because of digital code incompatibility. So for this part it is a guess on my part)
I certainly can change my DVD-A player to put out compatible digital code to my two channel DAC.
Hope your stuff works out.

Meridian speakers allow for direct connection with 2.0 "stereo", but require a Meridian processor for true 5.1 "surround". It's not complicated, but Meridian has their own way of handling processing. ;)

Think of the Meridian "digital" as simply having a DAC at the front end, and you'll see that it is a stretch to expect them to do decoding as well. You don't say which model you are considering, though. I have a pair of D6000's, and they accept both analogue and digital signals so, if you don't have separate digital outputs for 5.1, chances are you probably don't need to switch to a digital processor. This D6000 accepts both balanced and unbalanced analogue lines.