If you have an outboard power sup. addressing it may help. on mine, the audio is affected only by addressing it, not the preamp itself. I think I could turn my pre on it's side and it'd play well still. My pre has the BDR feet as OEM eq.
I've also heard from another owner of the same pre, that those boston Acoustic footers take it up another step by adding a greater spacial value.... though I've not tried them myself.
An "oh, BTW, DIY mdf" platform under the pre itself, also helped.
the most substantial and noticeable change came by the use of tube rings from herbie's Audio Labs. ...on the signal tubes... not the output... Well, they worked for me in two different preamps. And, yes, even the cheap ones made positive changes.
A good rack or preamp stand will yield still greater improvements... and a dedicated power line is beneficial too.