Speakers, speaker cables or I’m getting old…

What you're experiencing is the sound of Heritage Specials vs Harbeth.  HS are overly detailed and can sound harsh and fatiguing, especially brand new out of the box.  I've owned Special 40s and loved that speaker, even more than the HS. Harbeth are super pleasant sounding speakers, even on recordings that are less than perfect.  Sorry, but this has nothing to do with the cables.  I've owned HS and every model Harbeth makes, except for the 40 series.  I liked the HS at first, until I realized I couldn't listen for very long, and the music became fatiguing, just like B&W.  I would suggest pairing your Pass to a different speaker that creates a more satisfying presentation.  

@toddcowles while I'm not saying this is your specific issue, I have a local contact who's complaining about the exact same issue you are now and he also runs those same AA cables you have now, fwtw.  Coincidence, i don't know.  They did not have the problem until they ran those cables you have now. Will be interesting when you report back about the upcoming changes you'll try next.  If you plan to keep the HS speakers, I believe you can make adjustments elsewhere, maybe.  

Also, not to derail you too much, but what preamplifier are you running wiht the X150.8 amp?

I heard that amp at a show a few years back at a show with some efficient Zu Audio speakers, and holy cow it just sounded terrible (overly fatiguing) with the volume turned up. All I could think of at that moment if they were to continue to run those speakers, was for them swapping out the preamp and swapping out the cables for something a little more forgiving, perhaps.  Will be interested in your update after you swap some of that out and try others. Best of Luck. 

Great a miracle cable hunt to go with the Easter egg hunt. So is it fact, fiction, old age, stupidity, or placebo ? Yosemite Sam “I hate that rabbit”  that was another Looney Tune.

Cheers 

@ericeagleson I agree, I wouldn’t compare them, and both have special qualities that I adore.  I won’t agree or disagree with the cable comment, but I’ll share my experience when the the current $1/foot wire is swapped…I”m reserving judgement there.  I’ve never gone too in-depth with cables, so I don’t have an inherent bias towards any brand or thought position on it.  On my prior systems I invested heavily into Shunyata.  I swapped out the Shun Hydra setup for a Nordost QX4 and Qbase, that certainly changed the dynamics.  This time, I opted to go entry level on the cabling.  I believe I’ve spent a grand total of $2k on all of the cabling, including the Ethernet cables.  I would say this is really my first experiment/experience with an effort around taking time with the cabling.  
 

@decooney I don’t have their speaker cables running, yet.  It’s $1 General special running now.  I have their C20 power cables and will be running a set of their midrange speaker cables.  I’ll keep you updated.  I’m running the Pass X2.5.  I do know there is a PL fan cohort that abhors the .8 series.  I’ve ran the XA60.5’s and they certainly were very organic sounding, really enjoyed them.  The one note I would say is they are current monsters, efficient speakers will dance.  I did go with copper cabling.
 

Update, given what I’ve heard thus far and without a doubt, new speaker cables will improve it.  I can already tell there’s things I really like about this speaker and there are things I really like about the Harbeth SLH5’s, so I bought a set of SHL5+ XD’s.  

The mid-bass on these little puppies is excruciatingly good, esp for their size.  I’ll likely keep them for a bit, may build a second system out of them.  Again, thanks for the comments.