Have you listened to single driver speakers before? Yes, the Druids/Tones are not technically single drivers but they share far more in common with SDs than conventional speakers.
I'm sold on the Zu concept and have owned three of their models. I haven't heard Omega but I firmly believe in Louis and his work, as I've read probably a hundred posts at AC from deliriously happy owners.
Sound-wise, the Druid is undoubtedly the biggest speaker of the bunch. Tonally, it is quite even and I found it fairly insensitive to placement. It is definitely voiced toward the warmer side, which might be good or maybe not, depending on the 300B amp. Some 300Bs can be a bit syrupy and slower sounding, which could make for an overly idealized sound without proper incisiveness and jump factor. Druid bass is very fast, tuneful, and integrated with the rest of the speaker. If you get these, pay special attention to the floor gap at the bottom. If using a carpeted floor, create a hard surface to set the speakers on. Then, tune the floor gap accordingly. Never place Druids directly on a carpeted floor.
I haven't heard the Tones, but I know at least one person on the 'Gon had to use digital EQ to get the frequency balance where he wanted it. The sound had an overactive presence band for his taste. I don't remember what amp he was using with it, but amp/speaker matching gets Really Important with edgy single drivers. Again, I can't say whether the Tones are edgy, but this complaint parallels many regarding this type of speaker. If there is an issue here, I would think a 300B amp would be an excellent partner.
My opinion is the supertweeters on either of the Zu speakers will give you better treble extension than any of the Omegas. That said, I haven't heard anybody complain about the Omega treble and many have said they're not missing anything higher up.
Of the Omegas, they're all great. I like bass and I definitely would be looking to the biggest models Louis makes. His bigger speakers use 1 of 2 - 8", wide-range drivers. One is a hemp driver with a whizzer cone that he has personally developed with a driver manufacturer specifically for his purposes. The other is the Visaton B200 from Germany, another hemp driver that has gotten ungodly press over at AC. Do a search and prepare to hunker down.
Of these drivers, the hemp driver is reported to be more relaxed and the B200 more lit up. Think 2A3 or 300B SET vs. a 45. Personally, I would look at it as yin/yang. If you think your amp tends toward mellowness, choose the jumpier speaker, if the amp needs some taming, go the other direction.
I really like tube amps and single drivers. I think you're on the right path and there are probably no bad choices. You may look for something used to try, knowing you don't have much to lose in the deal. And, Zu's 60 day trial period can be extended to 90 days if for some reason you just can't decide.
