Had a great audition on the Uniti Nova, driving the B&W804D3. Previously I owned the 804D2 and now a 802D2, both driven by a NAP250. My verdict:
The Nova is an smart but expensive piece of engineering. It sounds wonderful in combination with the 804. It's operator-friendly, with a 'Favourite' button for your preferred ratio stations or other inputs. A nice feature is the HDMI input, which allows you to control the Naim volume via your TV remote, rather than juggling with two remotes.
Also the artwork on the screen is quite addictive. Suddenly the 'classic' line with its stacked boxes looks old-fashioned and so twentieth' century..... It's like comparing a Nokia with an iPhone .
The only issue I have is the shiny remote control, which is not as solid as the previous remote, and is extremely sensitive to fingerprints. Not an improvement.
I started this topic being concerned about the very low impedance of the 804, but this was no issue for the Nova up to 60% volume. In our medium-sized room there was not any need to go louder! So I have no more worries about the ability of the Nova to drive low impedance speakers.
The combination with 804D3 sounds wonderful. The sound stage is very precise with a detailed stereo picture. Positioning of instruments and vocals is very accurate, much better than the 804D2. When you're sitting close it's like wearing a headphone!
The 804 shows fantastic high's and mid's. Instruments like flute, violin, acoustic guitar, trumpet and all voices sound very natural. A great speaker for acoustic and classical music.
I found the diamond tweeters of the 804D2 and 802D2 (Diamond series) somewhat too bright/harsh, and have dampened them by putting a piece of cloth under the tweeter protection cover. No need to do this with the D3, the balance with the mid-range has really improved. Still, the overall sound impression is a bit forward/bright, so the system may sound better in somwhat dampened room (curtains, rugs etc)
Obiously you miss out some heavy bass/body, which becomes clear when listening at heavy rock, symphony orchestra's or grand piano's. For a more full sound you would need its bigger brothers 803/802 driven by a 250 or 300.
Overall this set is an improvement compared to SuperUnit+804D2 or 250+804D2 on musical refinement, sound stage and looks.