Casey:
I own the larger B&K amp (150 wpc . . . it’s >30 yrs old & working great) which, like the ST-140, uses mosfets for power. Though some criticize mosfets as less than ideally resolving (they harp on the "mosfet fog"), I beg to differ--music that isn’t hyped in the upper midrange and low treble to insinuate "resolution" simply sounds more like music. So I say if you can get the B&K, do it, revisions be damned.
I, too, do all my listening in a relatively small (13’ x 13’) home office using a nearfield configuration. With listening as close up as this, any component in the entire chain that hypes the music, makes it sound edgy and insistent, is going to give you a headache. These are the nearfield facts of life.
As for class D, I’m a big fan--but only because I did my homework (hours and hours of it) to find the few class D amps that are A. affordable for me; and B. said by at least some users as being "musical," or at least, pretty nice to appreciate music with. I ended up with 3 class Ds that sound pretty wonderful:
A. Wyred 4 Sound ST-500: This 250 wpc amp is based on ICEPower, which some deride as not state-of-the-art. Too bad . . . it sounds great to me.
B. Bel Cando 500S: Also 250 wpc based on ICEPower. Resolves a little better than the W4S, but truthfully, the W4S is more than resolving enough.
C. Bel Canto 600M monoblocks: These 250 wpc monoblocks are based on the newer NCore technology. They sound rather amazing.
Bel Canto is fairly expensive, even used. Wyre 4 Sound less so. But the prices will never get as low as the B&K, so it’s all kind of academic.
PS: The types of music you listen to are sometimes recorded "hot" in the studio, which makes it even more important to avoide edgy, bright compoments in your stereo rig IMO.