@audiovicker , I had a similar issue. My 300B wasn't cutting it and I have high efficiency speakers (about 100dB) in a good size room (16 wide, 24 long, 10' high). I tried push pull (Primaluna and Carver Crimson) to decent effect, yet I still missed that 300B magic.
Atmasphere (Ralph Karsten) educated me on 300B topology. One of the issues is that although you get clean signal through the first few watts, you quickly move into its distortion profile. Maybe the first watt of that is harmonic goodness, but the point is we never really get 8 useful watts a side out of a 300B SET.
At any rate, in December I bought a Willsenton 800 805 tube version integrated. This is about 45W a side, CLASS A SET. The amp weighs 100lbs. The stuff inside it is high quality. The 805 tubes are driven by two 300Bs and the gain stage is 6SN7s. I love this combination. Reportedly, yet unconfirmed, the Willsenton is made in the same factory as Line Magnetic. I have run across two people who have preferred the Willsenton 805 to the Line Magnetic--but most say they are very similar. I haven't heard the Line Magnetic 805 though.
This amplifier has changed my outlook. I'm not sure what loudspeakers you're running or how large your room is--yet 45 watts a side of Class A power is nothing to scoff at. Reviewers have driven speakers far less efficient than I have with the Willsenton.
If you are in the Chicagoland area (or care to be in the winter months :) ), PM me and you can stop by and put the amp through its paces. I have vinyl, SACD/CD, and Qobuz via Roon sources.
Some folks say the Willsenton owners are making a statement with this, they're top of the line amplifier, and that their profit margins are too low on it. That could lead to issues in the future. But, they have US authorized service.
I ordered the amplifier, paid about $2850 with shipping and customs; it was at my door in 5-7 days of purchase. You will need 2 people to lift the beast. Nothing about it feels cheap and it exudes quality (ok maybe the tube cage is a little basic). Highly, highly recommended. I could've saved a lot of money playing around with other amps had I bought a Line Magnetic or this previously.
Final note: If you have a smaller to medium room it can heat the room after 3 hours of playtime. There's no way I'll be using it in the summer months so that's a huge downside for me. Still worth it though.