Typically, No-Rez/BH can make a semi-dramatic difference depending on what the stock material is. Improving Caps is also quite noticeable if you were to compare tracks back and forth...and much moreso than improving the quality of wire. However, that too, depends on the stock material used. Since I'm not familiar with the details behind the HT3s, I can't say much there. There are all sorts of upgrades available for various speakers...better binding posts, wire, etc. Caps and cabinet material are likely going to give you the biggest improvement out of anything.
With nice electronics, you'll get more of a benefit out of higher-end caps. Blackhole should improve the sound quality in any system if the stock material is just basic stuff. Altogether, you're talking about a..idk...5% improvement in SQ? (if one were to quantify it...)
Just my .02...