switching between two amplifiers; issues of power

A couple of caveats. I had (still have) a similar situation. I have a pair of tubed mono block amps that I use for serious listening and a SS amp which I keep as a backup or use when I just want some background music on but don't want to put hours on my tube amps. Both are connected through a Beresford switch box to my single pair of speakers. When I want to swap amps or do an A-B comparison, its simply a matter of throwing the switches on the Beresford. DO NOT CONFUSE THIS WITH A SPEAKER SELECTION SWITCH BOX. The Beresford is specifically designed for the exact purpose of swapping amps to a single speaker load. Also I believe i read somewhere that tube amps should never be left on without a load connected. This is consistent with the Beresford design the circuitry of which  includes dummy load resistors to prevent a powered on tube amp from seeing an open load. 

J.Chip

Well, mr decibel is one who’s input I trust for sure. We don’t run an hour in the high nineties for many reasons... this isn’t a lecture but watch your ears !!!! Royals is a high power density track ( give me a bit and I will post the RTA of that track on my virtual system page - I was recently using that to help a fellow audiogon member size his amplifier ( with less efficient speakers than yours )
your hour requirement drives duty cycle. In an A/B amp, you need a beefy power supply, lots of output devices and a way to get the heat out. Look under the hood on the 225 and it will indeed be lacking, so I retract my recommendation. I would point you to Van Alstine IF the class D disappoints. I will let you know when I put up the RTA photo - it is a great track for taxing a system.

Yes, my use of high nineties was for projection out of windows into my backyard. With alleged 98db speakers, I didn't think this would be a problem (for the Nuforce), but it did heat up (considerably) over the hour... 

Within the 12x14.5 room of primary listenership, Peaks are more in the high eighties, or lower, for most of my listening. I should try Royals in that context, but truth-be-told, I'm fairly tired of the song. It's more a sonic biceps flex than anything else.

Just received Trio Jeepy CD from the culture of Amazon, and the hints of the original space of recording come through. Love the distance-impression of the sax, out on the left, the chunky and springy percussion off the right, the sweet double-bass in the midst. The Nuforce is perfect for this. 

I'd be interested to learn more about how the RTA of Royals interacts with an amp. 

@tomic601 You mention, "Van Alstine IF the class D disappoints." I did a search, nothing came up that matched... 

Try Audio by Van Alstine

OK I posted the screenshot of RTA with Royals. A fun track for sure to flex the bass a bit. You can find it on my virtual system Poverty Bay Sound. Have fun, i hope your search is going well.
Jim