What equipment upgrades or tweaks will improve the sound of drums?

I suspect your source material. Do you get good drum sounds from other recordings? Elton was/is a big pop star who has sold millions of records which have been massed produce for an audience that is largely ambivalent about tonality. To the record company he was a cash cow and they probably did everything they could to maximize profits from his recordings. Quantity over quality, not to mention that his early recordings were probably mixed and mastered for AM radio. With the exception of the kick drum and possibly a large floor tom the frequency range of most drums is the same as the male vocal range so if your system reproduces good male vocals is should reproduce good drums provided they were recorded, mixed and mastered well.

The 17-11-70 live recording is fine with lots of energy from Elton and powerful bass & drums. Clean enough (free of distortion) to play quite loud. 

For newer drum & bass try e.g. William Parker - Drum & Bass Interlude.

Thanks for all of the suggestions and comments.  One of the first things I did a while back was to deal with the power issue.  I noticed that when a dehumidifier ran, sound sucked.  So, a Torus Power Conditioner, dedicated line, etc, reduced those issues.  Isolation also key. Symposium Stealth Iso made a big difference.  I have not tackled all of the phase issues with the sub.  The recordings....all Better Records versions of Hot Stampers.  At first a skeptic, but damn, they can't be beat.  Agree with the Mofi dissapointments with other recordings.  I have had good drum sounds, just looking for the extra snap, bite and boom.  I like to think I'm pretty close.  I have borrowed amps with more power and still believe this could be offer a major improvement. Will be playing around with tube rolling and all the other little additions you have suggested.
Thanks all,
Udog