McIntosh c1100 vs audio research ref 6se vs Ayer KX-R

I’d do the Mac for sure. The ARC preamps don’t always work well with Mac amps as the output impedance of the preamp is a bit high for the relatively low input impedance of most Mac amps. You can always try it and see. 
George 

Why is low impedance of a Mac going into an arc preamp with a high impedance a bad thing?

It has to do with the ability of the preamp to properly drive the power amp. What you want is low impedance on the output of the preamp and high impedance of the power amp. There are tons of articles written by folks way smarter than me so google can be your friend here. From personal experience the ARC preamps have a bit higher output impedance as is often the case for tube preamps of around 200 ohms. If you look at measurement from some of the reviews however at the higher frequencies they can go up to 2000 ohms almost. That said with the McIntosh amps around 22k ohms that can lead to a loss of some of the detail.  With amps that have input impedances of 100k ohm or more that isn’t a problem any longer. That said ... it will work and some folks like the sound but I wasn’t a fan when I tried it for sure. 

Tough to find a good expl on google.  Important issue.  Thanks for info.  This is why marketing info from sellers needs to improve in explaining low vs high impedance relationships between components.

Careful what you ask for :-) this is off the VTL site and explains it quite well I think ...

Probably the second most critical interface connection in the audio chain is the interface between the preamplifier and the power amplifier. The interconnecting cable can also have an impact in this interface, especially if the cable is very long or is highly capacitive.

For the best and most predictable results it is often best to use pre- and power amplifiers from the same manufacturer, as it stands to reason that these components would form the most synergistic combination together, allowing the design engineer to make the best decisions for each component.

If different makes of pre- and power amplifier are being considered it may become necessary to compare the output impedance of the preamplifier and the input impedance of the power amplifier. Generally for full frequency response it is advisable to match component impedances with a look-up factor of at least 200.

This is not to say that the components would not work together. The audio industry does have open architecture and a common interface between components. However what can happen with disparate impedances is that there could be substantial frequency response roll-off between the two components, particularly in the low frequency bass region. This is only potentially a problem when considering a tube preamplifier to drive a solid state amplifier, as many tube preamplifiers have very high output impedances, (designed to drive high input impedance tube power amplifiers) and most solid state amplifiers have low input impedances. Sometimes a high output impedance preamplifier can be very sensitive to the capacitance of the interconnect cable, which tends to roll off the high frequencies also.

The combination of tube front end for voltage amplification and a solid state power amplifier for current demands can work very well in delivering the best that both technologies have to offer. This is provided the preamplifier is designed to drive the lower input impedance that solid state amplifiers typically present to the preamplifier. The VTL TL2.5 and TL5.5 with their output impedance of approximately 200ohms are both designed to be able to drive solid state amplifiers down to 45k ohm and 20k ohm input impedance respectively, with little or no noticeable roll-off in the bass.The TL7.5 will drive any power amplifier through any reasonable length of cable with predictable performance, with only slight bass loss into the punishing 600 ohm studio standard.top

Cheers!

George