This Might Not Exist, Any reasonably priced, smaller speakers with 100db Sensitivity?

Tekton is a good choice.call him tell Eric what you want he can heip.enjoy the search

I have a Triode Labs 45 monoblock Set amp putting out the most glorious 4.5 watts I’ve heard into large Joseph Crowe horns (105 db) in room. 
 

while these were being built for me, Troy loaned me a small wide baffle back loaded horn speaker that sounded magnificent in a near to midfield environment; so nice with the set amp that I bought it for my second system after I got the big horns.

look at his website and then call him; he might have something perfect for you.

If you don't mind DIY you could install a Tangband 1772 driver in a sealed box and supplement it with a tweeter (both crossed over properly to avoid comb filtering). Its 97dB and in a reasonably sized box (bigger bookshelf) would go to 45-50Hz.

I'm doing exactly this right now for a set of monitors in my electronic music lab at home. The amp driving them makes 5 Watts (class A PP tube amp; much cleaner than an SET of similar power) plenty in the room I'm using.

Any smaller speaker like this will need a sub.

This may be another option that’s not too big, probably overpriced a bit (gotta pay NYC rent, unlike the Tekton dudes who are set up in a farm middle of nowhere Utah)

https://ojas.nyc/collections/frontpage/products/klipsch-x-ojas-ko-1

Seeing as though you have jumped head-first into the flea-powered amp rabbit hole, keeping with the theme I would seriously look into a pair of Volti Audio Razz speakers. Sure, Heresys will work, but I’m guessing you want to spend more money and get something that won’t feel awkward in the company of the Triode Audio Labs amp you have sitting there.

Note: you can get gorgeous finished ones for $7500 and up, but you may want to continue being the contrarian you appear to be and get the unfinished ones for $5500. Slap a coat of gray paint on them and be the envy of your neighborhood!