In need high-efficency speakers

You need to figure out what your priorities  are. With high efficiency  your giving up bass for same size speaker. Your amp should have plenty of oomph to drive many types of speakers as long as your not headbanging. Try to hear as much as you can. 

Hi , I have Zu Omen MkI, Klipsch Heresy II’s, Klipsch KG 1.5’s , And JBL 4312A’s. I use either a 12 Wpc Had Inspire , Dynakit MkIII’s ( 60 Wpc ), or a Vintage Marantz 2226 receiver . Without a doubt get the Omens ! I love mine . Sometimes Zu is short on used drivers and installs new ones on the Dirtys ( so I’ve heard ). I have heavy carpet and run the provided spikes . Even with 12 Wpc the Bass is good . I purchased some solid 3” thick Timbernation spiked bases and it sounded terrible . Went back to the spikes . Of the 4 pairs of speakers , I like the Heresys the least . If your interested , I’ll make you a deal . I read a review on the Zotl 40 Wpc and the reviewer loved it with his Tekton Double Impacts . But for $750 , I purchased a pair of pristine Zu Omens in walnut , and will never sell them . At that price you can get the MK II UPGRADE and buy some nice speaker cables , I run Anti-Cables level 3 and Morrow Level 5 Interconnects . My room is 15x20 with a 12’ ceiling . Hope this helps , Mike . 

13blm,
Yes I'm aware of the trade offs. I'm slow and sure before making purchases. When we're no longer able to be content with the lower volume for movies/tv I'll make the plunge. But the Klipsch and Zu are at the top of my short list.

Mjcmt, given that you’ve purchased a pre-owned amplifier, I’m wondering if the reason the sound "hardens" when the volume control is turned up past the 12 o’clock position might simply be that some of the tubes might not be in good condition.

In any event, consistent with my earlier comments it seems to me that buying new speakers to compensate for the fact that turning the volume control up high enough to utilize the majority of the amp’s power capability is not possible without significant sonic degradation, while not first determining what the root cause of the problem is, would not be a good approach. And if the root cause of the problem ultimately cannot be determined, I would consider replacing the amp, not the speakers. As I indicated earlier, you are probably not using more than about 6 watts of its specified 40 watt capability.

Good luck. Regards,
-- Al

Take the amp and the speakers to an audio friend’s place (or to a dealer) and test each out with other gear.

Choose a course once you’ve figured out the issue(s).

It's more advisable to do this than have a friend bring the gear to your place, just in case the issue(s) are not related to the speakers or the amp. That way you will have a starting point.