OK there I know someone who has a MB 400 OK. He says that he uses 6L6 for powertubes in it? What gives? I thought that the 400 had 6 6550 tubes in it and the 400+ has 12 6L6 tubes in it? Am I missing something. Also how would a MB 400 with the 6550 tubes compare to a Aguilar DB 359?