I just purchased an RBX4 A2 and find that it could probably benefit from the same strings I use on another bass I have with a fragile neck: D'Addario Long Scale Medium Light Round Wounds. My guitar repair technician has always recommended that model for basses with a thin or fragile-feeling neck.
I used Dean Markley blue steels on RBX A2 when I had it back in the days.... and it sounded pretty good.
I use Rotosound SS strings on mine. People are right that nothing sounds quite like a fresh set of Roto's, and on a growly jazz type bass like that, they sound absolutely killer.
I used the D'Addario Chromes Flat Wound Regular Long 105/50. I don't think it's the best choice, but I am a flat wound guy, so....
I removed the flat wounds, because the sound tube setup actually caused a kink in the strings, and the chrome strings, with a 50+ lbs tension, is not a good choice for this bass guitar. I saw there was a tiny amount of warpage that was not there before, because the E string only has 40 lbs of tension, and the extra tension on the sharp side caused the warpage. I switched for D'Addario EXL220 strings, they are much softer and work very well on this bass. I still have to readjust the bridge for height, because of the lower amount of tension in the strings.
I have 2 RBX5A2 basses and Elixirs are by far the best I've used. I've tried DR's and D'adario on these basses and the Elixirs have the best sound and tension for the RBX basses.
Ken Smith Bass Burners on the one I had. Took some of the harshness out of it. At least the 'harshness' that the stock strings give it. I didn't like the stock strings at all.