I should have been clear that I was shopping for a desktop/tower machine -- both Apple and Dell probably have more powerful Xeon or Threadripper servers with price tags way beyond my means. Some of those CPUs alone cost more than my whole new machine!
I'd suggest the following ranges of PC hardware to play the full Nancy sampleset without leaving anything out. There will be other PC combinations that could do it, but I'll keep it straightforward. Assume the highest Hauptwerk 7 audio quality settings, 96k sample rate, and 1024 or 512 buffer size.
Memory: At least 96 GB, preferably 128 GB
Processor: At least an AMD Ryzen 9 or Intel Core i7-12xxx or i9-12xxx generation 12
Disk: At least 2 TB of internal SSD and 2 - 4 TB of external or internal SSD for backups, install files, etc.
For processors, you're looking for a desktop CPU rated over 30,000 CPUMark and over 2,500 ThreadMark on this list:
https://www.cpubenchmark.net/CPU_mega_page.htmlYou can select "desktop" in the right hand column and sort by clicking the CPUMark column arrows to see if a proposed CPU is in the range Nancy works well in (over 30,000).
Even with the 40,000 or so CPU Marks I bought, I have to set the polyphony limit carefully for full Nancy at 96k. It's a lot of long releases. Outside of polyphony testing, I actually truncate the Close, Front, and Middle releases to about 3 seconds, leaving Rear at full length, because it seems too wet to me otherwise. A personal preference only. That saves CPU time and allows for a higher polyphony limit in practice.
I don't have all the answers, so your Hauptwerk PC builder might have better ideas for you. But you can at least sanity-check the proposal against the ranges above.
I bought from Dell because I understand what I'm getting from them. Mine is an XPS 8950 with liquid cooling, i9-12900K 16 core processor, 128 GB memory, and 2 TB SSD disk. I already had two 2 TB external SSD drives. Sale price was just under $4000. You'd expect to pay more for build and setup/tuning services that I did myself, of course.
Edit: Yes, any Xeon dual CPU 12 core model Mac Pro built in 2010 - 2012 was very underpowered compared to today's Intel Core i7 or i9 gen 11 or 12, AMD Ryzen 9 or Threadripper, and Apple M1 processors.
Edit 2: I should say that Nancy with only 2 of the 4 perspectives (mic positions) can be very enjoyable and massive-sounding. I've been using it that way on a 17,000 CPU Mark PC with 64 GB until now, and it's been great. Wanting to run at the new higher quality Hauptwerk 7 audio options is what had me looking for a bigger machine.
Edit 3: There's a current Mac Pro (28 core Xeon) with about the same performance as my new PC. At about 4 times the price. Ouch.