The crossover in the picture is using decent air-cored inductors, but the capacitors look cheap. Instead of changing the values, replace them with something quality. Even the cheapest MKP's from M-cap would beat these. find a friendly shop that allows you to try different values, start with same values as they are, just do not solder them in, if you intend to change them, use clips.
Also a piece of foam around the HF driver is not going to do anything. Try gluing immitation leather (or real!) on the entire front face, as used on Sonus Faber speakers, it looks better, and has more effect, but only if you are suffering refraction, otherwise leave it alone.