I had the same Horizon/Clearaudio Aurum Beta S combination. I found upgrading the counterweight to the Expressimo was worthwhile. Switching to incognito was more of a mixed bag- it brought out a bit more detail, but was a lot edgier, analytical, and had more emphasis on surface noise. The incognito-wired arm was fine with other cartridges so I don't think it was entirely break-in. The stock Rega wire is smoother and more laid back- seemed to be a good match with the Clearaudio in my system.
Also note the the Michell counterweights do not work well with cartridges as heavy as the Clearaudio- I was not able to extend the heavier weight far enough for the Clearaudio to track at 2.1 G- not a problem with the expressimo.
Also note the the Michell counterweights do not work well with cartridges as heavy as the Clearaudio- I was not able to extend the heavier weight far enough for the Clearaudio to track at 2.1 G- not a problem with the expressimo.