First Watt J2 & speaker pairing ?

The J2 has a 20dB gain so from that perspective it is similar to the XA-25 from Pass Labs. I owned a J2 and an F6 which has a 14dB gain but a 25wpc into 8 ohms and 50wpc into 4 ohms spec which is also a characteristic of the XA-25. Yet neither sound like the XA-25. I now own an XA-25 and it is fantastic. With that said, the J2 when paired with a Rogue RH-5 pre having selectable gain (3dB, 12dB, 16dB) there is magic to be had with any 8 ohm nominal speaker capable of 90dB efficiency and above. I used all 3 of the aforementioned amps with Focal Kanta No.2s, Mirage M760s, and Wharfdale Linton Heritage speakers (6 ohm nominal). The J2 will drive any of those speakers well but since all of those speakers have a tendency to dip down into the 3 ohm range at lower frequencies you should focus on 8 ohm speakers that have a flatter impedance profile. The J2 will lose potential volume since the wpc dips along with the impedance. Someone mentioned Tannoys and they likely are the better candidate as their 8 ohm speakers have a relatively flat impedance profile. Late in the J2 game I picked up a set of Moth Audio Cicadas with 94dB sensitivity and 12 ohm impedance and everything seemed to gel, so to speak. I was impressed with the sound that came out of those single driver speakers and the amp really seemed to be at home with them.

A Zu Audio speaker with a higher nominal impedance with higher sensitivity would probably work very well with the J2.

However...

I did have a pair of Zu Audio Soul Mkll RevC speakers that would get very loud with the J2, F6, and XA-25 but they seemed to put forth a sound like an empty concert hall, almost like an echo, that I could not tune out. They did not seem to mate well with any of the Pass amp designs. But...when I connected those speakers to my custom built 15wpc tube amp they sounded great. All else the same, only the power amplifier was changed.

Bottom line: Find and audition speakers with efficiency ratings above 90dB and impedance of 8 ohm or above with a relatively flat impedance curve.

Read the reviews of J2s and you'll get al the guidance you need.

If you want this brand, I would switch speakers. But I heard the DQ10 clear back in college and they sound great. I think they were $500 at the time. Efficient speakers tend to be larger.

I have a Pass XA25. A used one would be about 1000 more than a Fw, Very simple circuit, single ended. It has reserve AB power to about 80 watts. Even with that, during a review, it was not recommended for Magnapan which is similar in impedence to DQ10.

@pmm, I totally misunderstood your post. Apologies sent! 

@mfm22, I think you need to determine what kind of listening you do. If you have a huge room, and like to listen at 100db +,  this amp might not work.  My J2 is in a 13x9x8 room.  I listen at the loudest, 85ish db’s.  For my needs the 25 watts is more than adequate. 
    I find the sonics of the J2 very addictive.  A huge soundstage is a priority for me,and the J2 fits in wonderfully.  If a lower power amp works in your environment,I can’t recommend it enough.