Does any one have experience with a high-end amp switch or the Luxman AS-55

Am I better off just swapping speakerwire bananas at the amp-side? (I know that I need to turn OFF the tubed amp especially when doing so....)

I have used a Luxman AS-55.  It works great although I prefer the AS-50R remote model for comparing speakers because I don't have to get up off my butt to do an A/B comparison.

Audio by Van Alstine also makes a very good comparator.  It's probably the best of the bunch but the Luxmans have worked great for me.  Good sound and no damaged gear.

$550? Swap bananas. Or if you want to be very cool get a high current 4 pole relay with a 25 volt coil, a 25 volt power supply and a hand held toggle switch. Cost you less than 100 bucks. Wire it all up in a metal or plastic box and change speakers from your seat. 

It looks like that switch is designed for a single amplifier to switch between multiple speakers - I'm not sure it can be used to switch multiple amplifiers into one pair of speakers.

Thanks @br3098 and @cleeds 

The unit's documentation shows it can be used to switch between amps.

@br3098 I appreciate the heads-up on the remote version. I couldn't find the Van Alstine product you described on their website -- is it a custom unit?

Fwiw, I also heard back from Luxman Global who indicated that the switch was indeed good for the L-509x (what else were they going to say!), and that I should use good jumpers/cables.

The AS-55 and AS-50R can absolutely be used to switch one amp source to up to three sets of speakers or three amp sources a single set of speakers.  Just remember that it's a switch designed for speaker output only.  It's a brilliant design and is done well.  I don't think I could build myself with similar quality for what Luxman charges for these devices.

Cables?  I would just use your standard brand of speaker cables for the longer runs.  The short jumper pair to the single amp (or speaker) can be almost anything.  I prefer inexpensive silvered copper wire jumpers but use whatever you like.  If they are under 24" you could almost use coat hanger wire.  Almost...

Here's the link to the Van Alstine device: https://avahifi.com/products/abx-switch-comparator

The problem of using a switcher to select between a tube amp or solid state amp connect to one speaker is most tube amp is not safe to operated without a load and can caused blown output tubes and transformer !!
Accident happens if someone forget to turn off the tube amp before switching!

A safer way is connect a 150ohm 10watt resistor on the tube amp each output terminals.

Or use this design to switch amps on the fly :

https://ucarecdn.audiogon.com/d3ee951e-1868-4baf-986b-d1b2f92cb2fe/-/autorotate/yes/

The 3P3T rotary switch must use a shorting / make before break contact style switch like a Grayhill 44A45-03-01-03S, which can switch 100watt@4ohm or 200watt@8ohm.
R1 is a dummy load which can be 25 to 50 ohm and rated 25watt or higher will be sufficient.

A switch such as this, no matter the quality, will decrease detail, damping and overall sq, in my experience. Several high end dealers I worked with, used switching in the lower level sound rooms, but never, in a million years, would use switching, when using the better higher end gear. I would not use it.

Well, like it or not, a lot of japan made high end amplifier come with built-in speaker selector! Convenience vs compromises :)

I was honored to hear from the designer of the Comparator at Van Alstine Audio, and read a few reviews and blogs about the unit. Seems like a great Hifi fit for my needs. In his words,
“A lot of effort has gone into making the ABX box transparent. It is DC coupled from input to output, so there are no coupling capacitors in the design. The only thing in the signal path are relays and an Analog Devices digital potentiometer, which is defined in the Analog Devices data sheet as a "digitally controlled variable resistor". The relays are high capacity 10 amp units, which are many times what is encountered. The digital potentiometer is a necessary evil as it is absolutely imperative that any valid comparison be made at the same volume level.” — Dan Kuechle 

Beresford makes a quality line of amp/speaker switch selectors that are both affordable and provide dummy loading to protect your amp if you forget to turn it off when switching. 
http://www.homehifi.co.uk/S/selector.htm

J.Chip