Jacob,
If you decide to dabble into buying a few more tubes my recommnedation would be to track down a pair of 5998s. They used to sell in the $100-$150 range on Ebay, but looking now I don't see any good options. I'd be on the lookout for them anyway. They were far and away my favorite in the Menace, which is essentially an Extreme taken to the Extreme. 7236s would be a solid second option but as you're finding, even cheap-as-chips 6AS7s sound really fracken good.