I am thinking about the 400 or 400+. Which sounds better? I have been told that 6550 tubes are better sounding. Not as mushy? More of that tubish warmth and glassy highs in the 6550? Sorry I know this has probably been asked a thousand times. Also planning on using this mesa tube head with two Aguilar GS 1-12 cabs any thought on that too? Thanks gang.