Amuseb,
Nice speakers! I`d really like to hear those hornings one day. These speakers are quite efficient and you have more system gain than you require.
I had this problem initially (my speakers are 94 db at 8 ohms)with my linestage having 20 db of gain.Could`nt go pass 10 oclock volume setting for most recordings(too loud). I had the builder lower the gain to 10 db and things have been fabulous since(ultra low noise floor).Lowering the gain in your ARC preamp will solve your problem.
Regards,