@decooney,
I tried a bunch of different signal tubes including NOS Mullard CV4003 tubes and some other exotic tubes. Although it did change the flavor, that grain was always evident. Unfortunately, I sold the amp when I bought a McIntosh MA6600 integrated which I use daily in my office system. Next up will be to get a pair of Cornwall IV’s to try in the office system. I’m currently using the new JBL 100 Century speakers in the office system with a single SVS sub. While I love the sound, I have an itch to try the Cornwalls. I use that system to try different speakers.