New listening room need help deciding on new speakers

Regardless of which direction you plan to orient the system room treatments can do wonders for a smaller space, making it behave like a much larger space.  
if orienting on the narrow side I’d suspect first reflection point absorption would be key.  If orienting the other way front and rear wall treatments would be a bigger deal.

i have a smaller space and with substantial room treatments it has proven to be an exceptional space.  I found a used pair of Vandersteen Treo CT’s just above your budget and with the right amplifier (zero or minimal feedback), they’re quite special.  

+1 Try what you have and work from there.

I know your amp well having owned and loved my Osprey paired with Harbeth 30.2 XDs and a pair of REL subs.

I’d stay with what you have and dial in the room first.

PS then maybe try some tube rolling if you have not done so already. 

Love the bookshelf sub concept.  For the upper end I would look at Studio Electric, Buchardt, Ascend, SF and Totem ... as well as other superb suggestions offered above.