I have a Yamaha A 500 Integrated from 1983 that I just matched up with a pair of used Jamo E 800 bookshelf speakers that I bought this week. The sound when bi wired is incredible for a speaker that retailed for $400 a pair in its day.
But... I just noted the A 500 is rated for 8 ohm speakers and NOT 4 ohm speakers which the E 800's are. This is according to the A 500 manual. No mention is made NOT to use 4 ohms but NO mention is made that they are compatible either.