Can you specify your current CPU model so we know what you're working with now?
For example: Intel Core i7-10700F, Intel Xeon W-3365, or AMD Ryzen 9 3950X are the kind of names I'm asking for.
Unless you have a recent CPU, you can expect to need a new PC to support a current generation processor, since motherboard sockets, cooling and power requirements, etc. change fairly quickly. I know you, like me, aren't a do-it-yourself PC builder.
Before investing more money,
1. Are you sure your Windows tuning is correct according to the user guide pages 308 - 310? Any Windows update or upgrade can mess those settings up, so you should check them all.
2. Are you using 48k sample rate and 1024 sample buffer (512 if the latency really bothers you)? Running at 96k and/or small buffer sizes really sucks up the CPU. The audio is almost as good at 48k with the Higher audio engine processing quality setting. I can't hear the difference.
3. What's your polyphony limit on Nancy? Does the polyphony meter hit yellow or red when the CPU meter hits red? Have you truncated Close releases on Nancy, since you can't hear them unless Close is the only perspective you use, and you said you're using three? One of the possible ways to make Nancy less CPU-demanding is to truncate releases on Close and Front, relying on the huge reverb in Middle to give the acoustic impression, and don't load Rear. All those long releases demand a lot more polyphony than most PCs can deliver.
4. What's your polyphony limit on Aristide, and same question as 3? I don't find Aristide v2 demands as much as Caen Surround, but are you still running it with added convolution reverb? That can cost a lot of CPU if you add reverb to a number of stereo buses, which might be worth turning off for a test.
Polyphony limit is meant to be set low enough to keep your CPU from glitching, so you shouldn't actually have audio glitches, just voices dropped as you approach the polyphony limit. Since you have glitches, your polyphony limits are set too high for your CPU.
I just turn off my speakers and play a lot of big chords at full organ with subcouplers on Nancy while watching the CPU meter, and keep lowering the polyphony limit until the CPU meter stays green or yellow, never red.
If you do that, then live with it for a while and see if dropped releases and notes are bothering you.
If the polyphony meter stays green during full organ, you shouldn't hear much dropping out at all. If it goes red, and you've tuned Windows properly, then, yep, you need a faster PC.
(Forearm chords still send Nancy into the red on my PC, but I don't play music written for forearms...)