the Meridian G68 digital outputs are proprietary and are meant to be conected to Meridian active loudspeakers. In addition to the digital signal, they require a secondary communications link that probably does things such as control volume.
The Mini-DSP module is more of a low cost band-aid if you want to enhance a current system. I think you're better off just replacing the Marantz 7701 with another processor that does all the EQ / Crossover / Room Correction that the Mini-DSP does. Emotiva XMC-1 (possibly with Dirac room control)?
Outlaw 976 has 10-band parametric EQ for each channel.
There are lot's of others, but depend on your budget and if you want automatic room correction of some sort.
The Mini-DSP module is more of a low cost band-aid if you want to enhance a current system. I think you're better off just replacing the Marantz 7701 with another processor that does all the EQ / Crossover / Room Correction that the Mini-DSP does. Emotiva XMC-1 (possibly with Dirac room control)?
Outlaw 976 has 10-band parametric EQ for each channel.
There are lot's of others, but depend on your budget and if you want automatic room correction of some sort.