B/W 702 s3

As for adding a sub or two, would you recommend mono or stereo subs.  I do have a mono sub jack on the Rotel RC 1590 MII

Definitely two subs you can run off the pre outs on your 1590, and disregard those who say subs are just about more bass because they’ve no clue what they’re talking about.  Good subs implemented properly not only extend bass but also produce better/more solid imaging and an expanded 3D soundstage and can be transformative.  If you otherwise like what you’re hearing from bass on up then adding subs could make a lot of sense.  You could do something like a pair of SVS subs that include a helpful app for integration and offer a 45-day risk free trial period including shipping both ways, and a pair of SB1000 Pros is only $1140 and will get you down to an honest 20Hz despite being only 13” square.  Free to try and may tell you all you need to know.  

https://www.svsound.com/products/sb-1000-pro-subwoofer

There is my room.  That took me a awhile.  Cool post image site.  Thanks

I see both (1) room issues (both sidewalls need absorption-drapes?-to tame reflections) and (2) speaker placement issues (perhaps depth perception of photo but appears speakers are very far away from listening position vs how far apart they are and they seem too close to front wall).  I agree with others that there may be a synergy issue with the  Rotel although it seems powerful enough to drive them.  Experiment with placement/room treatment first--yes, subs can help but those speakers have enough bottom for most music--someone also mentioned REW--you can also download the Audiotools app on your phone and use your phone mic to walk around your room using the acoustical analysis tools to see where your room modes and nulls are--it's close enough to REW and you don't need to purchase a mic.  

B&Ws need high current amplification. You don’t need to bi-amp them with rotels. You need a high quality amp, good cables and some acoustic treatment. Look into Coda amplifiers. They’re high current design. Coda No.8 should be good. 
I would also recommend limited range bass traps in the corners behind the speakers. GIK Acoustics makes good limited range tri traps. This would help improve bass definition. These are good speakers that simply need a good amp.