How about the smaller Omega speakers which are about the same size as the RB-81:
Omega Speakers Products
Zu Tone:
Tone™ Bookshelf Studio Monitor - Zu Audio - Phone (800) 516-8925
Another Zu speaker:
6moons audio reviews: Zu Audio Druid Credenza
Here is the beginning of a thread I have in my archives from the Asylum speaking to this subject-- "Is 90dB eff enough?":
Audio Asylum Thread Printer (note that not all these would be considered bookshelf size) and another note: The "I have" is not me, below;
I have lots of experience with monitor speakers in the 92 - 96 dB range run by low powered tube amps, which I have summarized below. I suggest you not get hung up on a single characteristic like sensitivity, although I might guess you will do better with somewhat more sensitive speakers. There are a few monitors in the 92-96 dB range that do fairly well with low powered (2 – 8 watt) SET amps in a moderate size room. Bass won't be great, but you can get good midrange and good imaging. I have a 12 x 10 home office with a REL Strata III, so bass is not an issue for me although I don’t use it most of the time. Here are a few monitors I have tried in the last couple of
years, in order of my personal preference:
"1. Coincident Triumph Signature UHS, Extreme Version - neutral presentation, excellent
imaging, speakers disappear, wonderfully transparent, smooth and highly detailed mids, bass
not as deep, but tighter than other monitors
2. Reference 3A MM De Capo i - good clarity and imaging, smooth midrange and nice tight
bass, highs good, big soundstage, slightly rich sounding
3. Cabasse Goelette 500 - slightly forward, outstanding clarity, good strong midrange, wide
soundstage, highs very good, tight bass (can change woofer phase for more bass)
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4. Reimer McCullough GS - Big, slightly warm sound, best bass in a monitor, detail very good,
good smooth mids
5. Coincident Triumph Signature UHS - recessed presentation, excellent imaging, speakers
disapear, smooth and detailed
6. Galante Raphpsody - warm & sweet midrange, limited highs, imaging only good, detail good,
sound veiled compared to the best
7. Omega TS1R - slightly forward, good mids, good highs, lack transparency of best monitors
but a great value for the $
8. Omega Super 3 - slightly forward, clean mids, ok highs, fast sounding, bass lacking
9. Adire HE 10.1 - good midrange, lacks detail and highs, nice bass
10. Klipsch RB-35 - good bass, but mids too fatiguing, even after 30 days of break-in
11. Loth X BS 1 - forward mids, weak highs, shouty and fatiguing