Vintage question HK 680i v Pioneer sx980?

Hi, I have a HK 680i that is very impressive sounding as most of the mid 70 to mid 80s HK gear seems to be. I should point out I am running very good AP speaker cables and ICs as well as having the unit set up to take my VH Audio power cord. Things that were not taken into account when it was made back in 1980, cost $650. I base my view of the sound on the fact that I have owned things all the way up to Bel Cato, Exposure, Vincent, NAD Rotel and many others.

That old I HK stuff is pretty good but I love the look of the Pioneer SX980 and have a chance to get one for a reasonable price. Despite working in the CE biz in the 80s I have not heard a Pioneer SX-50 or SX -80 since 1979. The last one was a SX850. I know people say the 50 series has a richer more full sound then the 80 series.

The question is how would a SX 850 or an SX 980 compare soundwise to the HK680i twin power?? Was anyone ever had them side by side?? Is this worth even messing with?? Thanks