Does impedance of a speaker change when one bi-amps?

There are companies offering DIY loudpseaker kits, the drivers and speaker-level passive x/o parts, along with required enclosure (or OB baffle) specs, provided. You make the enclosure (or buy one with the specified internal volume; Parts Express sells good ones) or OB baffle, and install the drivers and x/o. One such is Danny Richie at GR Research, located in Texas. He is a renown x/o designer, doing work for other speaker makers. Very high performance-to-cost-ratio speakers. Danny specializes in high-sensitivity designs (and is a fan of OB's) for use with low-power tube amps. Details on the GR Research website.

@steve59 

I found a review at Sound Stage mag. Looks like a nice amp. This is interesting, from the review   https://www.soundstagehifi.com/index.php/equipment-reviews/934-hegel-music-systems-h360-dac-integrat...

  Like its predecessor, the H360 boasts a whopping 250Wpc into 8 ohms, or 420Wpc into 4 ohms. Its damping factor is over 4000 -- four times that of the H300. It should have no difficulty driving just about any pair of speakers it’s hooked up to.

I see he is impressed with daming factors that are very large and 4 times larger is, 4 times better?. We know 1000 or 4000 makes no difference. 

If you trip the thermal something has to be done. Can you now put your hand on the heatsinks after extended playing? If not you are still too hot.

The h360 has been in my system over a year now and only shut down the one time. I owned a pair of kef R105/3's for over 20 years and they had 93.5 db eff so compared to the salon2 at 86 db they played considerably louder with less power. I read the review and every other I could find after hearing the h360 at home and being so impressed with it, I had never heard of the company and needed to know more. When it shut down it was only warm to the touch and I really probably shouldn't be chasing the ear bleeding levels those old kef's could reach anyhow. When the music is coming out so clean it's easy to get in trouble with the volume control.