The Atma-Sphere OTLs will definitely give you a lot of what you find magical about SETs with the dynamic punch and bottom end that you crave. This will be the case if your speakers are an appropriate match, meaning 8ohm load or higher. With 4ohm speakers, you will need an autoformer, such as the Paul Spelz zeros, to get the Atma's to sound anything like they should.
Another type amp that reminds me of 300B, but has a bit more punch is a 211 based pushpull amp, such as the Consonance Cyber 211s that ultravioletaudio imports into the US. I think these are about halfway between the sound of a 300B and a traditional EL34 or KT88 type sound (i.e. big, warm, punchy).
Disclaimer: I own Atma-Sphere amps. Cheers,
Spencer