What's the best Line Magnetic SET amp?

Thanks for the response. And yes, you've nailed exactly what I'm asking. I'm not even displeased with my current setup, I just have upgrader's itch.

I am also considering changing my speakers, but I barely know where to start with that. :/

I am a little confused by what you are saying. You already are using a transmitter triode SET from Line Magnetic and are wondering whether a different transmitter triode SET also from Line Magnetic would be better and a "step up" from your current amplifier.

I have seen the 845 SET by LM, and the reviews on it are good, but I would be skeptical that you would find a significant difference between the two. I have seen reviewers who say the 211 is "warmer and fuller" than the 845, and then I have seen others that say the opposite. You are driving a speaker with average sensitivity (89dB). An 845 SET would have less power. The 211 (218ia) has a higher rated power. Have you considered changing your speakers instead of your amp?

Have you considered other tube amp makers? I am not sure of your budget, but given that you are cruising in the rarefied air of high-voltage transmitter tube amps already, there are SET offerings by NAT from Serbia (they sell in North America) that use other tubes. I have only seen them in reviews, but they are well reviewed.