Yamaha's last 2-Channel amplifiers and part of the ToP-ART series: Total Purity Audio Reproduction Technology. This far flung acronym doesn't mean Yamaha's previous amplifiers were crap but the early 1990s called for more marketing, hoping to maintain sales in what had become a gradually dwindling market...

Build-quality isn't equivalent to a B-2x, sure, but still rather healthy: fully Dual-Mono with 2x 33,000µF and 2x 35,000µF caps, two 335VA transformers, Class A stages, HCA output stages, a base made of two 1,6mm steel plates sandwiched around a damping material, select componentry and gold-plated bus bars and terminals . The damping factor is huge as well: 350 between 20Hz and 20kHz ! The result is "Power ohne Ende", although not as distinguished as, say, a B-2.
The smaller MX-2 is basically the same amplifier with less available power and no damping between the two base plates ; the MX-2 was export only and not available in Japan.