A / B Switching

I don't think so.. Macs are tough.. You need a second amp. If you want to really A/B it right.. The OLD Mac way.. Was A or B or A and B. I like both ways.. It just takes a second amp.. A/B amps switches, are not a great idea.. like you said.. Different impedance matching problems with just a switch.. If the speakers are the same, impedance, that problem is solved, with an A/B switch, BUT the CRAP switch and cables.. LOL Your still stuck with that..

You're better off with the preamp A/B and a second stereo amp.. SQ wise.

Regards

I used to use a Niles Audio SVC2, high quality, controls volume also

https://www.ebay.com/p/1475699276

Thanks guys for the advice. My listening room isn’t huge.  I may have to end up running the DQ-10’s off a separate system in another, larger, room just based on the space requirements

You will more likely burn up the switch. They are all rated fairly low.

way overkill - but this thing works and it is quite a truth teller!

https://avahifi.com/products/abx-switch-comparator

iirc niles made a line of regular speaker selectors... ok, not great fidelity but did the job safely

btw,

It isn't good to have spare speakers in a listening space, they passively react to vibrations generated by the active speakers. 

This is good stuff - thank you to everyone.  So if I’m following correctly: Mac C 28 out to the Mac 2105.  Also out of the C28 to Adcom GFA555.  From there as normal to speakers. The C 28 preamp doesn’t have any type of selector to switch between amps (?). It does however have the RCA posts to connect another amp.  I’m a little new to vintage audio so please forgive any obvious questions 

OK let me look.

That one uses a Main and Remote push button option on the front Same as ok.. Don’t just push the button, while blaring either, I don’t know what will happen.. OK.. Turn it DOWN then push the button.. Just to be safe.

Remote and Main do not have independent volume control, (usually)
Tone control on one effect ALL the amps..

Route one set of RCAs from each, The mains and the remotes to the two different amps.. That Adcom be careful. With some of them and I’m not sure on that one..

The GFA 565s the DC voltage goes high and blows voice coils on the bass drivers..It has to do with a 6db first order XO there is NO cap in the path (speaker side). They (Adcoms) have leaky Dcaps and causes the IC boards to short.. A MESS. BUT Adcom is a great amp for the money. I still have 6-8 around here..I like the 5800s, Power house..Good sounding..when you get it warm..

It is easy to check DC offset, just google it, and see if the 555 is prone to.. Save you some money..Some bass drivers are tough to come by..

Have fun..

Regards..