Ground source hum

Please do not float any ground. I understand your situation, but floating grounds is quite simply defeating the circuit protections designed to save your life. You are now a better ground than house ground because it isn't there anymore and you are toast. Find the problem and fix it. One suggestion is to place all your lower level electronics through the same device/power conditioner/isolater and the amps through their own separate dedicated line back to electric panel. In other words, if you have two amps, each amp should have their own dedicated line to the panel and they should be on opposite sides of the input line. Most houses have 220volts coming in and separated in the panel. Therefore, one amp runs to one 120 input and the second one goes to the other side and do not share neutrals in the outlet boxes. Also, the other electronics should have their own separate dedicated line. So, the pre-amp, tuner, turntable, cd player, etc, plug into a conditioner and that has a dedicated line to the panel. Also, check your cables, sometimes the shield is tied to the signal return, not good, or the signal return is lifted and floating also. Sometimes the manufacturer ties electronic's signal ground to house ground and that is not right and there is your ground loop. But floating ground is simply dangerous and if a fault happens there will be major problems. Fix the problem, don't mask it.

enjoy

Turns out the fix was a little more straight forward. I use a Power Wedge 116 for power distribution. I had the Pre and Amp connected to the same outlet section. Switching the pre to a different outlet dropped the hum by at least 75% (only noticeable at less than 12" from driver). I suspect the remaining hum is as Ojgalli suggested, EMI between the Amp and crossover. I will try to move those further apart and see what happens but even as is, the hum is fine.
Thanks for the compliments Ojgalli

I assume this is too your Orions. I had a problem with hum also. You may have already done this, but since you've ruled out the cable, check your outlets for proper grounding. It's not uncommon, even in newer homes, for the wiring to be incorrect. Also, how far away is the ASP from the amp or other electronics? It is sensitive to EMI, you may need to keep it several feet away. I had both of these problems in my old home. After I moved the problem was the cable and the only fix was an isolation transformer on the cable.

BTW, love your version of the Orion—stunning!

Are both amp and preamp on the same circuit? If not, put them on the same circuit. Have you tried changing the preamp>amp interconnect? If not, try this. Are you sure it's not cable? Have you disconnected your main incoming cable line?

BTW, I think if I had to float a ground it would be on the amp, not the preamp.

Good luck,
John