Bookshelf speakers for small room

Harbeths are great speakers and it appears the P3 is a real gem according to many. With a cheap thousand dollar SVS SB-3000 you'd have full range with a sealed tight sub, and the ability on the fly (via remote) to adjust for a customized loudness setting for low level listening.

Otherwise I think you must have a loudness or bass level control unless low level bass is not desired. Bass drops off tremendously at lower levels, at least what is perceived audibly. I don't think the old loudness controls were designed for bass-heads; they facilitate more enjoyable low-level listening.

And if the budget is truly $15k I'd sure be shopping a lot more higher end bookshelf speakers as well. I know some who like 15k of electronics hooked to 2-4k speakers but that's pretty low bang for the audio buck IMO. Start to seriously blind audition electronics and see what you can really hear or identify. It's usually not much when compared to a loudspeaker upgrade will provide for your money. I think many of us forget what makes the single most difference audibly...

As mentioned, this is a great project so have a lot of fun and good luck!

For small rooms and near-field listening conditions, the Kef LS50 is an easy recommend. The coincident/coaxial driver design provides a single point source of sound and excels in close-listening situations. I also listen at low levels (SPL) and am very happy with my choice.

In my home office set up I use a pair of Martin Logan 35XT biwired connected to a Bluesound Powernode 2i (I previously had the Powernode 2) and Definitive Supercube 2000 sub. I’ve this set up since 2015 and upgraded to PowerNode 2i in 2020. I also use Roon, Tidal MQA for streaming. Radio Paradise now streams MQA free of charge and can give you a chance to listen to MQA stream for free. I can honestly say I’ve enjoyed the sound over the years in a 13’ x 11’ room. I use a  Dragonfly cobalt Audioquest DAC for headphone listening in my office powering Audeze LCD-3, Sennheizer HD-650, and Master & Dynamic headphones. 

harbeth p3’s work great nearfield, and at modest volumes, as do the larger models

also consider smaller proacs, classic spendors, and fritzes

good luck