I like with subs that I could add DSP and such alleviating possible issues in such a small space.
Bingo! That’s what I’d do. Trying to deal with larger speakers in that room could be tough, and a pair of small subs like the SVS SB1000 Pros that include integration software will not only make dealing with bass much easier but also get you down to an honest 20Hz for only $1150 (and a generous risk-free trial period) that makes a huge difference outside of just bass and you won’t get near with larger Harbeths. I think a pair of P3esrs with a couple good, small subs could be sublime, although the Rainmakers are also excellent speakers so adding subs to them may be all you need unless you crave that Harbeth sound. Hope this helps, and best of luck.