Realistically, only in near perfect environments would you have a hope of detecting any difference in quality when using or not using a splice in the wiring. Yes, there are a dozen ways to do it, and if you really want to go through the headache of soldering and the whole nine yards, then by all means do so.
But, at the end of the day, if the connections aren't environmentally exposed (outside), then you won't have any issues with basic wire nuts from your local hardware store. They are really cheap, and work really well.
If the splice is outdoors, especially to outdoor speakers, make sure to get some decent outdoor speaker cable and I would use waterproof, direct burial type, wire nuts.
Ran across this site the other day and it seems like it covers some nice bases...
http://www.outdoorspeakerdepot.com/