I think if you much prefer the little bear, you would more prefer the ta10 because of it’s tube properties, and you could also experiment with tube swapping to further dial in the sound you prefer
The other stack I mentioned is good, but I think you would personally enjoy the ta10 more because it would change the sound more.
The AD18 imo isn’t enough for the rb42 imo, and you would want to get a more solid amp. You could run the line out of the dac of the ta10 to a speaker amp
The AD18 would not be sufficient for really loud volumes in larger spaces, but for this size of room, I think it may work out fine. Of course, more power would work better, but would also cost more. If OP can fit the Emotiva BasX A-100 monster in there, that would be perfect. 
Or a topping pa3 would work just fine as well
I think given the two, I’d go with the topping… Particularly with size constraints
Edit: Scrap that, it wouldn’t even fit length wise.
How would the PA3 compare to the Micca OriGain or SMSL SA100?
Also, how do the RB42s compare to the MB42(X)s?
So the Pa3 is a step above the Origain and Sa100 imo because it can deliver a very clean signal with good power for the price.
The rb42s are also a step above the Mb42xs imo. The rb42 has better imagining, soundstage, detail, bass, mid-range, and treble. I would say it’s a fairly large upgrade.
So PA3 is $110, but cleaner signal and more power
OriGain is $80, only one input and no frills
SA100 is $74, smole, bt5 and digital readout
RB42s are $150 as compared to the MB42Xs $80, but better in sound quality all around.
Pretty much imo. There are other speakers you could consider but I don’t know if you would have the space
A 990 brother who doesn’t mind the highs I found one holy shit. I also find that the t2’s and t3’s highs bother me more. I would say the k5 proor if you want a separate things topping d10 with a liquid spark or atom. But unlike the liquid spark more with the DT 990 they pair better. Out of my collection the 990 seems to be the most consistent thing for me to reach for.
That’s not bad, I would just wonder where they would fit, as that’s a decently large speaker. The pioneer bs22 would also be something to look into
The bottom area where I would more likely stick them, due to the extreme size constraints up top, the area is ~15" (38.1cm) tall x 29.5" (74.93 cm) wide, and ~20" (50.8 cm) deep
What if you considered the iLoud Micro monitors, would those fit on the top? They are very impressive for their size, have bluetooth as a bonus, and you could feed them with a dac amp combo
They might… They are 90mm wide, and that JUST ENOUGH to fit next to the monitor (~95mm on either side)
Lol, it might be a tight fit, but that could be something to consider, those things are pretty great imo
I’ve found a pair that’s used $182 shipped, so it is an option
That’s a pretty good price, and when you factor in that now you would not need an amp, it’s a good deal imo. You could get the ta10 and a monitor volume control, and then feed the dac from the ta10 into the monitor control and then to the ilouds
A monitor control would be like a jbl nano patch + or other line level control
So looking like iLoud Micros and TA-10?
That would be a pretty great setup in my mind, but you might also want to get a volume control for the speakers
Fist thing that popped into my head was the Emotiva Control Freak, but I’m guessing it’s been discontinued.