I have speakers that only accepts single ended spades or banana ends. I have gotten a speaker cable that has banana ends but are biwired. Can this be converted to single ends without causing sound degradation, if there is such thing?
Or is there an accessory out that that can adopt to both types of end .
Your advice is always appreciated.
If you insist on using those cables that don't match your speakers, switch one set of bananas to spades, tighten down the spades, slip in the bananas, and you're in business. FWIW, in ancient, utilitarian times many banana pins incorporated female openings so the user could piggyback them to his/her heart's content.
Purchase some open stock Audioquest Type 6 or other decent cable, strip it to the core with NO insulation, shape into a small U and bridge the two sets on each speaker. Tighten down the connections and use bananas on the speaker cables. I just did this with my pair of Missions and they sound much better than the stupid bar bridges they sent with.

Also, if you REALLY want to improve the speaker, internally wire the cabinet by soldering same kind of wire from the crossover network to the tweeter and woofer eliminating the poor push pin connectors most use. Big improvement for 45 minutes work.
Rock's appraoch is valid; you can safely combine in this way & it may work out very well, or a different approach may work better. Only experimentation in YOUR rig with YOUR cables will tell. There are NO absolutes in this hobby.
WBT0645 bananas are stackable...