Flat back, how would you describe the difference in sound between the two elements bridged and the two elements sent to seperate channels? Have you tried running the two elements into the two channels of your focus? And I hear you about the tube amp. I once sat in on a jam session on my upright and sent my realist into the electric bassists' Aguilar db750 and 410 cab. It wasn't that it was loud, it just filled every nook and cranny of that place. Best my bass has ever sounded!