I am a long time Spica owner, and Angeluses have been my speaker for 9 years. I have been looking for an upgrade and it hasn't been easy - the Angelii are that good. Many speakers perform better in some areas (usually the bass), but I haven't found one yet that unequivically matches or beats them in every way. (I keep looking though - there are a handful thsat have come close)
The Spicas have more bass than most people realize. They are very clean and tight from *about* 40Hz to *about*80 Hz. It seems to be in the 100 - 150 Hz range that they are weak. On the plus side, this is the range where a lot of speakers have been difficult to position in my room. The Spicas can be put anywhere and they'll sound pretty good.
I agree that their treble is better than most people realize, because it integrates so well with the midrange. Cymbals have some real crash and weight to them - many speakers give you a delicate tweetery haze thsat floats above the music, maybe more delicate detail, but not as well integrated.
I agree that adding a subwoofer is the way to go. It is important, though, that you get one that can play well at fairly high (for a sub) frequencies, like 150 Hz crossover. It's kind of sad to do this in a way, because the Spicas bass (when it shows up) is so well done, it's a shame to cross it over. I have had good luck with a set of Entec LF-20s. I would recommend at least 2 (4 is even bettter) to keep up dynamically. If you want something cheaper, you might want to look for a used velodyne 10" servo controlled sub. I had one home new in 2001 (can't remember the exact model). It was more dynamic than the Entecs, but didn't go as low, or as flat. But still not bad.
I use MIT cable Terminator 3, and the previous owner was also using MIT. Kimber might also be a good one to try; I think they are wired internally with Kimber.
I find amplifier quality is more important than power. I have found the Pass Aleph 3 (30WPC) to be an excellent match to this speaker - better than more powerful Classe, Acurus, Meridian, Golden Tube, or Proceed amps. I have heard that tube amps go well also.
You have great speakers. If you can live with their shortcomings, their strengths are world-class. Sorry if I ramble, but I LOVE these speakers!