In Lampi news, the UK distro and I tried Justin's RK 300b, my PX25 at his place with KR05 pre, Yamamoto pre, and Thoress, Cube Audio (14w EL84), Yamamoto 45 and KR VA 200 power amps. The latter KR and Thoress were used only on his fantastic Emme speakers, the Yamamoto and Cube were used on his small DIY horns.
The PX25 was consistently better than the RK 300b with all combos where the KR recti and the masher was used. At Justin's too I had preferred the PX25 with his active pre, and preferred the Lampi 45s with his Airtight passive pre.
I then changed to the Ayon 5u4g recti. Immediately, the RK 300b sounded the best, and the PX25 did not sound good.
Overall, the combo of Ayon recti + RK 300b was tonally better, more air, and better midrange, suitable more for vocals, violins, woodwinds. The KR/masher recti + PX25 had a bit more ooomph, and was as good on some tracks, a bit less on others. I would keep both. Very different. We also tried the Ayon 32b which was nice, but you can't leave it on for too long as the Lampi is not built for it...if someone wants to use it they will need to customise their Lampi to deliver a different setting.
We could not compare the RX PX4, but will do so at some point to the PX25 and with the Ayon recti. Will also try on the Pacific at some point.