I think it's something that you have to try for yourself.
My suggestion is to try to listen on different time of the day.
If there's different experience, then you might go down the road finding power conditioner.
And also, try to remove all wallwart (iphone charger, other phone charger etc) from your house when listening. I found this effect on listening hd800 as the noise from wallwart really bother me even it's from my daughter bedroom (maybe different noise on different location of the world, I don't know for sure). But worth a try.
Hope it help.
Im using a APC H10. Imo, power management is something you should seriously consider if you've got spikes and sags. I have electrical issues in my home-particularly my room, lights shutting on and off on its own as well as other phenomenons. The APC H10 is a line conditioner as well as a voltage regulator and it does a fantastic job given those mysterious problems vanished. Its gives you peace of mind knowing that your investments are protected and fed a clean consistent power. As for SQ, it provided a better blackground, you wont get mind blowing improvements.
Thanks for your thoughts. I'm thinking right now the next upgrade I should do for the HD800 is my amp-- I've been happy with the Woo WA3, but by all accounts an amp upgrade would let the Senns show more of what they can do. Among other options, I'm thinking of the WA2...