Can I use an isolation stand with an isolation pad?

The first thing you need to figure out is if the noise that is bothering your neighbor is from mechanical coupling of the subwoofer to the floor or just the sound waves passing through the floor.

The former can be addressed by isolating the subwoofer. The latter can only be addressed by reducing the volume of your lower frequency sounds (i.e. less or no subwoofer).

My guess is that it's like @glennewdick says and you'll have to turn it down, forego the lower frequencies, or find some other compromise with your neighbor.

@geoffkait : said " I would know which springs to buy."

I bet you do. I'm sure you can send him to just the right web site too. With very very special springs.

He also said:  "I could be wrong."

Geoff, we all know you don't believe that.

Are you channeling glubson? If so you’re doing an excellent job. Newbies have a propensity to sass their elders and want to take charge and move out. But move where? 😁 McMaster Carr - supplier to the stars ⭐️ 

@geoffkait : " Are you channeling glubson?"

I have no idea what you'er talking about. But I'm sure you do and that's all that counts.

"Newbies have a propensity to sass their elders..."

Are you an old man Geoff? It certainly doesn't come across that way...(read sarcasm)....

" McMaster Carr - supplier to the stars"

Same stuff, right? Well, without the magic and the voodoo.....and insane prices. And as I'm sure you can attest, its the high price which really produces the desired effect...............

Whoa! You are good at the back and forth. Very ouch! I might have underestimated you. 🙄