Sub Pairing With Harbeth 40.3 XDs

from what I heard, for the most part, subs are cheap thrills (cheap subs). Listening fatigue will be off the charts if it’s too deep. So far I heard two types: powerful, in your face subs I don’t like or subtle subs I can’t hear (and sometimes I got it right.) I am waiting for an ELAC to try it with a remote.

@grislybutter 

Good point, my subs are pretty great and you can adjust so not "in your face" 

Subtle subs = what's the point? agreed. 

All good points. It’s hard to explain and I presume more knowledgeable or experienced folks would be able to describe it better. My old sub can be considered as poor as it is either too "in your face" or too subtle. If the bass sticks out too much, it’s unwelcome bass as the excessive bass which sticks out like a sore thumb is making more harm than good. If it’s too subtle, you can’t hear a difference. Good subs which are able to blend in well with the main speakers will make their presence felt, and the bass won’t feel like it’s detached or separate from the main speakers. In other words it’s a perfect seamless bass. A deeper, more defined and satisfying bass without anything sticking out too much like Home Theater the-bigger-the-better bass.

I had Harbeth SHL5+ with 2 RELT9i and the sound was very big and punchy.  I am well versed in technical subwoofer integration and ultimately the best I could do still had compromises.  A subtle but noticeable slowing down of the micro dynamics and transient speed of the main speakers, easily heard when the subs were switched out.  An occasional overbearing bass despite perfect level matching, basically either too loud or not loud enough as if the levels could not be finely enough tuned.  Granted I am a very particular listener and you might find these issues a compromise worth having.  You may be best served with an amplifier that can grip the 40s so that they can deliver the bass by themselves which they are capable of.  A Rotel Michi for example.  

My final answer was a pair of full range highly efficient british towers with special flared bottom port for sub bass and they do the job well.