I have ancient Sylvania on one 300 SEI. the one is the office still has the originals Works fine with KR Audio, EML, WE and British Genalexs.
The big difference on this baby is through 300B, 6SN7 makes smaller difference.
True but metal sylvania 6sn7w or tung sol round plate 6sn7/68fg make a good difference too. You have some nice 300b. How are KR balloons - I'm thinking about getting those - in comparison to EML300bxls?
You have 2 300sei? You must really enjoy them. It's a pretty good integrated amp and I'm surprised they aren't mentioned much on this forum. If you use 6sl7n in the two driver positions you get a nice increase in gain too. I'm using 6su7 currently and genalex 300b -nice airy ethereal sound however my klipsch bookshelf speakers are the real weakness and need to be replaced- have to try with my sub sometime soon too.