The MAS7.1 was Zektor's top of the line and final offering before they branched away from those smaller consumer switches and into the bigger venue size switches. Universal optical disc players and HDMI kind of changed the game for the "need" for these kind of switches (although we still need them).
The CVS4 and HDS4.1 are identical switches (the CVS4 is the fancier version, but they function identically), and are the next step down from the MAS7.1. They are 4-input, 1-output, 6-channel analog switches (also handles digital optical and digital coax). For quad fans, they allow you to have 4 decoders funneled down to one group of input/output RCA jacks. I currently run two of the CVS4's in my set-up; one for descrete sources, and one for matrix sources. They are nice products.
There is actaully an HDS4.1 on the 'Bay right now (I have no connection to it), at a very reasonable price, and looks to be in very good condition. I was going to say I don't know how often the Russound QT-1's come up, but I'll be damned, there's also one on the 'Bay right now, the very one Quad Linda pointed out. They are crazy work horses of switching, though I've never owned one personally. Looks like the choice is yours right now.