WHAT HAS WORKED FOR YOU? ISOLATION PLATFORMS, FOOTERS, ETC. for a DAC?

I'm not saying that at all. Everything should be isolated, power supplies, line conditioners, DACs, etc.

Personally, I think that too many audiophiles knee jerk into believing they must put something under their components to isolate them from whatever,  In the case of my Ear Acute, I preferred the sound of it sitting on it's own feet to any isolation device(s) I tried, including the Reimyo wooden gizmos, which were quite expensive.  I think, in general, footers can "clean up" the sound, which is great if you are experiencing a tubby bottom end to where baritone voices are too chesty or whatever.  But from everything I read around here, far more people believe their systems are too lean and harsh, rather than too full and warm.  So all I'm saying is, try it on it's own feet  and  don't be afraid to say you prefer the sound to that of it sitting on cones or pillows or whatever.  Only your ears can judge this.  Trust them, at least a little bit.  

My answer would be in five parts -- based on extensive experience with two DCS stacks (Paganini, and Vivaldi)

Step one get that DAC on a stand pronto, has to be off the floor -- and never never stack the DAC on top of any other component (even another part of the manufacturer's own kit such as the DCS components)

Secondly improve the power cord to the DAC

Thirdly explore footers, I use Marigo Extreme F8 (expensive) -- the location of the footers on the DAC will have a large impact. In comparison with the stock footers (which are multipart squishy stuff and metal) the constrained multi-layer Marigo's sound much more relaxed, open and less congested -- not at all "lean". I also have had good results from bearing based isolating footers so you could experiment with these -- unfortunately as all will sound different the best thing to do is to get someone (like Ron at Marigo) who will loan you a selection and let you try them out

Fourthly consider placing a Shakti stone on top of the DAC over the transformer area

And finally look into the shelf itself -- I  still have the stock perspex GPA shelves under my digital components however they have been treated with Marigo damping discs

do you have a linear power supply, or switching?

Eric is steering you in the right direction - electrical isolation, ground loops and room acoustics will be far more important than acoustic effects on an electronic component

it is unlikely that a DAV would be affected by acoustic effects - easy to test by putting it in an isolation chamber or on a suspension

occasional substance abuse works very good for me.