Could either amp work?

One tube amp that may work particularly well with the decreasing-with-frequency impedance nature of the speaker (as shown in George's graph) is the Music Reference RM-200. Unlike normal tube amps, it's power output increases as the frequency decreases.

Here is an impedance graph (solid line) of the CLS IIZ
The dotted line is Quad 57

As you can see, it goes below 1ohm, a tube may sound dull in the highs with these.

http://www.justrealmusic.com/images/graphs/quadclsimp.jpg

Cheers george

You should be OK with the CLS's. I've heard them powered by amps that put out a lot less power than the ARC's you list. And I'm pretty sure that they weren't the z version either. The z's are easier to drive than the older models.

Hi 1985tqc, I own the Monolith 111's and have driven them with just about everything, big 150w monoblock push/pull UL pentodes, massive monoblock SE 805 DHT, big Mosfets.
While they worked with all of these still sounded good, it wasn't until I used a >150w bi-polar amp (big older Krell type)that can good great current that they came alive.

As for the Monolith 111 themselves, they are compromised in the bass, that Eminence driver they had made is not too good, doesn't go low enough and is a bit 1 note'ish and it's F/S is too high. I found a good sub that matched well to T/S parameters of the box was the old ACI SV12 this is a killer bass driver and suits well. Unfortunately it's no longer available it was too expensive to produce.

Here is a post I made on it.
http://www.martinloganowners.com/forum/showthread.php?16441-ML-Monolith-III-and-damaged-woofer&p=173694&viewfull=1#post173694

Cheers George