If you can't get a schematic, as Erik mentioned, the biggest improvement is replacing the series caps (in positive lead)....
It was mentioned to get rid of the Solens... These are only a decent cap, fairly neutral,they don't do anything terribly wrong, but as Good Polypropylene goes nothing special. Personally, I'd start with any caps that are in the midrange and replace those (especially Electrolytic or Mylar caps (The Solen are much better than both of those). I'd then take a look at the Series caps in the tweeter and replace those (probably the Solens). Most if not all caps that run to ground are most likely Electrolytic, You should be okay replacing any smaller values, but an Electrolytic of any size, I probably would not replace unless you do some resistance measuring. Otherwise, buy a decent .1 mfd or so Polypropylene, Polystyrene or Teflon and do a bypass on those Parallel caps (goes to ground)... Overall this should provide a very nice improvement without any chance of negative effects.
Good Luck, Tim