On using the setup for 70% movies left, right and centre speakers are required to enjoy to some extent. Adding a sub to this setup depends on the FS, BS or sat speakers and their ability to stage the sound. If you are looking for a adhoc setup and planning to upgrade later then BS XS 2.1 is an option you may audtion and consider on your liking.
Also Sonodyne BS may pair well with Marantz given the speaker's bright sound signature, I feel your AVR will not be able to bring the best out of Sonus 2605 as specs wise it appears to be under powered. Happy audtioning and all the best!
Recently i bought Marantz NR1601 and Boston AS XS5.1, the combination is pretty good, without any doubt go with Boston AS XS5.1 for 5.1 setup later you can add two good BS speakers for 7.1 setup as well music too.
I just got hand onto one NR1601 bought by my friend and connected to my wharfi combo, believe me the unit really rocks on movie and music front as well.
Though I feel, its bit less powered as compared to my SR301, but has enough in stock for the blast. Very nice AVR with tons of features good enough for another 10 yrs atleast if some one does not dream of 4K etc in INDIA......