Alternative to my P3ESR

These Proacs are a bit above your $2k price range but would undoubtedly flesh out the lower mids/upper bass much more and not a hard load for your amp.  The tweeters need to be at ear level though as the treble will roll off if ears are off axis by too much. 

https://www.ebay.com/itm/116989610234

Alternatively, at a lower price point these Silverline Minuets also go quite a bit deeper than your Harbeths and are also a fairly benign load for amps. 

https://www.ebay.com/itm/358063192946

Just a couple ideas FWIW, and best of luck. 

Thanks everyone, some great advice before I try swapping the Harbeths, and good luck suggestions if I do. 

@dekay makes a great point about adjusting crossover frequency and gain on your subs.  When I swap my Q7s in I have to adjust my subs accordingly.  I found that I needed to set the crossover much higher than I anticipated and am able to get them well integrated.

To pair well with a capable tube amp, you might want to consider the ATC SCM11 v2, which is known for its precision, imaging, and tight control. It can sound a bit analytical, but that character should complement a tube amplifier nicely to reveal micro-details and transient dynamics.

Have you considered that the amp might be the issue? The worst amp pairing I had with 2 different Harbeth models used KT 150’s.

What SS amps did you try?