I've only heard the VP-300B at a friend's home, driving Cain & Cain Abbey single-driver speakers with the optional super tweeters. As expected, the midrange was glorious, especially on female vocals. My concern was the lack of frequency extension in the lows and highs, something I've always felt was an issue with the 300B tube. For single ended triodes I much prefer the 2A3 and 6C33 tubes. To my ears the 6L6 variants have much better frequency extension, better dynamics and sound staging, sounding like the EL34 and KT88 to a degree. I use the VP-20s to drive a pair of Decware MG944 speakers and have been very pleased with the sound ... quick, dynamic, huge soundstage. I hope this answers your question. Let me know if you have other questions.
Reed