Hello. I use Fremont Blacklines, and I cannot tell the difference between the Medium and the Hard models. I buy either individual packs from eBayer LucysUkulele (she also sells eBay Kiwayas so can be found by searching that on ebAy), or in bulk from Elderly (free shipping over fifty buck orders). Others will likely mention Martin strings, which is what you likely already have on the instrument (unless someone changed them), and rereading your list, that's precisely what you have.
To ring the most volume from the modern Martins, especially the cherry 3, Aquila Nylguts (white) are also handy, but sometimes the nut slot has to be widened especially for the C string (but widening is not always necessary). I would like the contrast with that Katalox fretboard as my Fremont Blacklines are dark, just like the Katalox. I have Aquilas on several of my Martins, but not the Cherry 3; I have Fremont Blacklines on it for now. Frankly, I'm gong to try Aquilas on mine when I do change the strings someday (I don't play it often, so that might be in several years) so that I might achieve a volume closer to that of my vintage Martins. Best to you, SamUke.
My input is probably not going to be of much help, as I really like the Martin strings on my 2k soprano. I've various sopranos that I have different string sets on: an Argapa with Living Water strings (works so well), a custom Yew Davidson which is very mellow and warm like cedar (Fremont Blacklines which offer more punch over Worth clears whist retaining enough warmth and sustain)
I'll always keep Martin strings on the 2k, it just sounds so.....Martin