Using the miniDSP and choosing speakers with optical inputs rules out the M6 but could use Meridian 5000, 5500, 5200 or 5200.2...
What if any the 16 plus year old speakers can still be repaired by Meridian, perhaps 5200?
Meridian, in an interview, suggest 12 year old speakers can be upgraded.
Hi
None of the DSPs have optical or analogue inputs, so you'd need a controller of some kind as suggested earlier.
Although Meridian themselves no longer support older models, the excellent
MrTechGuy company are the official legacy support service. Ex Meridian service dept staff, so they have the expertise to do the job properly.
There are still some upgrade kits for DSPs floating around, but as it's all used market kit now, you'd be better looking for the spec you need, rather than an older model and hoping to upgrade it (usually more expensive to do that anyway).
Cheers
George