J Gordon Holt writes ...
"Grand Integra" is the name Onkyo has given to its line of perfectionist-oriented audio products, and the M-508 is the cheaper of Onkyo's two Grand Integra power amplifiers. (The flagship model is the $4200 M-510, reviewed by Larry Greenhill in Vol.8 No.8, featuring "high current capability," and rated at 300W continuous per channel.)
The rather bulky, but surprisingly lightweight (for its size and power) M-508 is a true dual-mono design, consisting essentially of two completely separate amplifiers on a single chassis. That it is not designed for ..."
https://www.stereophile.com/content/onkyo-grand-integra-m-508-power-amplifier
