Dazler, ... normally I don't recommend gear, especially speakers. Too darn subjective and controversial a topic.
In this case I'll make an exception because you listed PSB as a possible speaker choice. I suggest that you add Paradigm Signature speakers to the list. Paradigm and PSB are Canadian cousins.
In particular, the Signature 6s or 8s (version 3), plus a companion Sig. center. There are some terrific prices for pre-owned. And if you spring for a Paradigm SUB 1 or SUB 2, watch out. Your neighbors, wifey or significant other may put a contract out on you. You WILL absolutely ROCK the house!!! :)
Oh ... I agree with Paraneer. Pick speakers first, ... then the amp. OTOH, if you have a good quality, high current capable SS amp, you should be good to go.
Finally, the S8s are front and back ported. My S8s are about 2 feet in front of the wall. I think 18 inches would be ok, that's just about 5 more than what you mentioned above.
Let us know what you decide.
Happy Holidays.
Bruce