If it's anything like this, there shouldn't be any issue with snipping the RCA plugs off one end of each speaker's wire and hooking them up to your Yamaha. Start with the volume turned down low, and gently increase.
I'm leaning toward the headphone solution. It's going to look a lot neater. Perhaps I'll make some room for the Soundesign speakers and put them next to the BAs that hang off the Yamaha. When I have some time. Some time in the indeterminate future.Sound Design?
Uuuuhhh... you must be VERY sentimental!
Well, if it has a headphone jack, I would use a headphone jack to dual RCA adapter first if possible--adjust the volume of the thing so it matches the record player. Be careful, some headphone amps can clip the inputs on your AVR.
Not a big fan of connecting the amplifier outputs to the inputs of an AVR but there is a way to do it with some resistors inline or something. Google is your friend for that one! You must really like those 8 tracks...keep on truckin'!
If you want to use the Sound Design speakers, not a problem as you can use the RCA type wires (cut one side off, strip the wires back and connect to the Yamaha binding posts) You can also change the input terminals from RCA to the proper binding posts--Parts Express has them for $5 to $10 each if cutting/trimming the backs of the enclosures is something that does not bother you.
I have a shelf in my garage that holds my "Land of Obsolete Toys" like a LD player, Mini-Disc and a cassette deck and an old Pioneer silver face receiver. Never power them up as they just sit there as curious objects of Christmas Past....