You don't have the digital multichannel inputs on the 568.2, you would need the MM version for that. That being the case, the HD621 could strip the multichannel audio from the HDMI and give you four SPDIF outputs. Ideally you would put these into a processor, so that can use M's DSP for various effects and bass management BUT you can just run Meridian speakers from the HD621.

This is sort of "frowned on" as you miss out on quite a bit, HOWEVER, if you're playing Skyfall at good volume through 5 DSPs, it's really a very impressive movie experience (and hi-res film tracks are stunning).

You can do the same thing with a modified Oppo using a Vanity card.

It would help if you put the rest of your system in your profile to allow more accurate advice.