After sorting through all the choices, I finally settled on a huge pair of polypropylene 1000uF caps made for commercial power supply applications (solar power). I found them cheap on ebay. I got them custom mounted. All the highs and the details are there. Very well balanced cap.The value of the part can make a difference. There is more nuance to power supply design than initially meets the eye. If the cap values are too large, the impedance curve of the output of the supply might not be a good bypass at high frequencies even though the overall output impedance might be lower. If too small, bass might not be well bypassed. This can change depending on the performance of the caps used- better caps can often be larger values. But you have to watch your timing constants (as a general rule of thumb, the TC of the power supply should be at least an octave lower than the TC of the audio circuit its supplying, and not much more!) and if you have regulation, many regulators won't be happy with larger values (and might have shorter lifespans too).
The shunt film cap on the large EL never worked over the long term. Over time, the combined cap would sound more like the EL cap (I think the film caps I was using were still burning in). Also, the film cap values were too small relative to the EL cap to make a difference in the long run. As one might expect, no EL cap can stand up to a good film, and that goes for all of the best. For EL caps, I tried Mundorf, Elna Silmic II, Nichicon, etc.
This is the tip of the iceberg! I would not write off conventional electrolytics though; if used correctly they can perform as well as film caps. If. Used. Correctly. YMMV but IME we've had terrible luck with using more exotic electrolytic capacitors; they don't seem to work as well as more middle-of-the-road parts. Quite often they wind up sounding dark.