I got a relic tweed Blues Jr. Yesterday, and a lacquered tweed extension cab. I thought that the blues junior would have an extension speaker jack, but it only has the jack for the internal speaker. Can send the amplifier output into an A/b/y box, and select between the internal open back speaker, and the closed back speaker cabinet? Also, can I use the Y on the box and run both 8ohm speakers at the same time without amplifier damage? Thanks!