Do you see yourself keeping the ProAc for the next 5–10 years? If the answer is yes, then go with the P-4600. But if you’re likely to move toward speakers in the 95–96 dB efficiency range in the near future, the A-48S would be my pick. If your emphasis is on building your system around musicality, go with the A-48S. For maximum flexibility, power, and long-term versatility, the P-4600 is the way to go. Both amps are truly end-game pieces for anyone who tends to keep their gear for the long haul.
I don’t see any subs in your room. A well-matched pair like REL’s could be a fantastic addition — they would add depth, scale, and bring even more life to your setup.
When I added my Tannoy and Accuphase back in late 2018, I knew, I’ve found my forever components; the kind I could build the rest of my system around. Like @arafiq I’ve had my fair share of gear swapping… Accuphase finally got me off the merry-go-round 🙂

