Location, location, location! Don't spend a dime on 'stuff' until you have set up your speakers and listening chair as best possible. There have been a lot of posts on 'proper set up' and should be in the archives, both here and on AudioAsylum. Putting the speakers against the wall and or/a corner ALONE (And it appears you have done both!) could be causing your problem, but placing your listening chair is very important as well. Locating it in a bass node could cause excessive bass, albeit over a small frequency range.
Another issue to consider it the tubes you are using on the Primaluna, both small and large(power) tubes, which can make a big difference. FWIW if you haven't already tried them try some good linear 6550's or 6l6GC's, especially the latter if you want less bass but a good linear tone. I've used SED's and they are not fat! You might also try some Sovtek 12AX7LPS which have a fine mid-range and HF tone but are also not fat in the bass.
Another issue to consider it the tubes you are using on the Primaluna, both small and large(power) tubes, which can make a big difference. FWIW if you haven't already tried them try some good linear 6550's or 6l6GC's, especially the latter if you want less bass but a good linear tone. I've used SED's and they are not fat! You might also try some Sovtek 12AX7LPS which have a fine mid-range and HF tone but are also not fat in the bass.