LP playback is lacking - any ideas?

Cartridge mis-alignment in the headshell can create some of the problems you mention..is the Benz properly set up? Are you the original owner of the Akito? Could be some problems there...can't hurt to check. Good Luck!

Get rid of the turntable and buy a Linn Sondek LP 12. End of problem.

Are you using power conditioning? Dirty power can muddy sound.

Standing waves(bass) can make a system sound lifeless,small, congested. The gear you have is capable of at least 80%, of state of the art performance, if properly set up. Tube traps would be the fix, for that problem. DIY traps are very easy to make.

Could be anything -- dontcha love it? If the arm is set up properly, then I'd be tempted to look first at what is supporting your TT (you don't mention that) room as a likely culprit. Of course, if your CD player produces a similar kind of congestion, I might suspect your room.