Hey, I just got an used Yorkville XS400 head today, and it's awesome! It definitely beats the living shtuff out of the 400B I had before in terms of tone and versatility. I've been trying to look for a certain tone. I'll try to describe it as best as possible. It will be a gritty, aggressive, punchy in your face tone, with a lot of bite to it. I will be playing with a pick through a Stingray and a 2x10 + 4x10 (Both Yorkville as well). The type of music this tone would suit is punk. Right now, I think I've got the right amount of tube gain and drive, but it's the actual EQ section that I need to work on. The tone I'm thinking of resembles that of Mark Hoppus (don't hurt me, I like the TONE). Can anybody help? By the way, the EQ controls are Bass, Low Mid, Parametric Mid (150 - 1.5k), High Mid, and Treble. Thanks in Advance.