The Wharfedale Diamond 12.2 is the only stock I can find in South Africa - A bit above the price compared to the rest, but I might be able to make a plan.IMHO Wharfedale Diamond 12.1 are worth adding to your list. They perform really well for the price (link to YT review and link to another review), but note that they are deeper than the XT15 you have now.
Actually, the low depth of the XT15 makes them IMHO a really nice (passive) option for desktop systems such as yours! A lot of passive speakers seem to be quite a bit deeper so may be intrusive in a desktop environment.
Regarding your other candidates, most of them weren't measured so it is difficult to say how the might perform.
In most cases another speaker from the series was measured so perhaps that could give some clue (even if not conclusive):
- Monitor Audio Bronze 50 and 100 - I can only find measurements for the Silver series and those look solid, but that may have no relation to Bronze series performance.
- Polk XT20 (link to review) - Similar to the XT15 you have just bigger; for an ultra-nearfield desktop setup such as yours I don't see a benefit of going with a bigger speaker. Similarly bright too.
- Klipsch R50m - I can only find measurements for the R-41m (link) and that one didn't perform particularly well. Bright and a lot of resonances.
- Q Acoustics 3010i - I can only find measurements for the 3020i (link) and that one seems to perform OK-ish. Some resonances.
- Polk ES15 - I can only find measurements for the ES20 (link) and that one seems to perform pretty well. Main issue is a resonance from the port, but overall a reasonably balanced response.
I have noticed the WD 12.2 have good reviews, are the a newer version of the 12.1?