Don't know if anyone is still looking at this thread (which I found very informative as a newbie), but I thought I'd just report back now that my Yaqin MC-100B (4 x KT88's) has been with me for a couple of days.
It sounds amazing!! Okay, it's my first tube amp so maybe this is just me discovering that I prefer tubes to transistors, but I'm hugely impressed. A very full-bodied, yet smooth sound with lots of powerful bass...lovely. By the way, I didn't get to try the supplied chinese KT88's as one got smashed in transit. It's running with a matched quad of winged-C KT88's.
Anyway, to get back back on topic, it drives my B&W 804S speakers, which I believe are considered a difficult load, very well indeed. In 'ultralinear' mode (apparently 60wpc) there is plenty of volume (without clipping) available and the bass is very deep & powerful. There's a lot more of it than there was with my transitor amp, too...which is to my liking. No sign of the sound becoming confused and incoherent at higher listening levels. In 'triode' mode (30wpc), the amp still drives the speakers okay at lower volume levels, but I sense that it does struggle a little when asked to play louder . I prefer the character of the sound in ultralinear mode anyway, so that's of no concern to me.
But, even though I'm more than happy at present I guess I should still look to audition some alternative speakers, as maybe I just don't know what I'm missing!