Well, the pics of the back of the new G68 and G61R are on the Meridian website and while they both feature speakerlink cat5 outputs, neither have cat5 inputs and it looks like the multichannel digital inputs are no bigger than in the old G68's so they'll only be 6 channel, not eight.
it seems odd to me that they'd put a 4 channel smartlink on the HD621 and then have no compatible devices to use it with. wouldn't that just scream the most terrible planning?
we know that the G68 can cope with 6 channels of digital input on the main zone, and simultaneously another 2 channels via a zone, and the DSP's are supposed to be programmable for all sorts, rather than just following what was thought about years ago.
as someone who has no inside Meridian knowledge, or even any in-depth knowledge about DSP programming or audio processing.. it seems eminently possible

dave