ATC SCM 40As can be an endgame speaker. Owned a pair for 5 years and loved them. Only replaced by ATC SCM 50As.
The ATC 40s will reflect each upgrade you place in front of them. They particularly like the Gaia ll footers and XLR interconnects at the preamp side. I doubted that until I converted unbalanced to balanced. Of course you will need run XLR at the speaker side.
Sub is optional. I found them quite adequate, but then mostly listen to non-bass demanding acoustic and vocal artists. The attack speed on these is ridiculous. The immediacy of the performance is where they live.
Best of luck finding what works best for you.