Go and listen to NBL's, preferably in your own room. If the room can handle it, they will do things (refinement, smoothness and loudness) that SBL's cannot do as well.
Listen to a pukka CDS2 and see whether you feel that it takes your CD player closer to your excellent turntable. With your LP12 the results will be close.
However, if most of your listening is on vinyl, I would investigate a superior record player - listen to a Well Tempered Reference or Roksan TMS2 (you can use your Aro on this) or equivalent I still believe that a top flight analogue source is so refined and graceful and transparent, that even the best CD players cannot match this.
There is a huge difference between LP12's and the better record players out there! I don't think that CD will do an excellent system like yours justice, no amount of 500's can fix this!
If it was my money I would get a better record player first and then NBL's with six 135's.
Also you should make sure all set up issues are totally sorted (proper mains, stands, equipement placement and room treatment)
Have fun.