Question on tube rolling with Melody I2A3....

I recently purchased a Melody I2A3 integrated amp, and have been quite amazed by it's performance on my Reference 3A MM de Cappo-i speakers. The 6moons review on this amp is right on the money, and is certainly going to be a keeper for me. Have any I2A3 owners out there tried replacing the stock Sovtek 2A3s with other sanely priced ($500 or less for the quad) 2A3's with noticeably better results? I replaced the stock 6SN7's with some nice 1950's Sylvania green label 6SN7GTB's, and the results were greatly improved dynamics, detail and speed, with even better extension in the highs. If upgrading the 2A3's gives similar improvements, I will be an extremely happy camper! Any suggestions?
I have this amp as well and wonder what to do when the time comes to replace the power rectifier tube, the round one. It does not appear to be available and I don't think there's a dealer any longer for the brand. Any ideas? I love the amp.