Tubes and light weight bass

You bought the wrong tube amps, if good bass reproduction was a goal. Get something with some bigger transformers...a KT-88 based design.

Or, if your in love with your amps...try subwoofers.

Dave

what power tubes are you using in the Shanglings? I don't own your amps, but have been using EH 6CA7 output tubes with great success. They still have the fantastic midrange of an EL34, but bring some of the KT dynamics and improved bass. On top of that, they are very inexpensive.

Regarding your question to replace preamp: I find an octal tube based preamp provides superior frequency response and dynamics that a miniature nine-pin cannot touch. So you might want to consider keeping your existing preamp.

also see if you can back your speakers a bit more into the corners or against the wall - might get them to load up a bit that way