How does the Marshall JVM compare to the Peavey 6505+? I'm pretty much a valve-amp virgin, lolz. I know quite a bit when it comes to tubes (which is weird), but regarding the amp themselves, I'm clueless. I know I'm definitely looking for an amp that hosts 6L6s. Can the Marshall change from the stock KKs to 6L6s, or is that a no go?