Vintage Yamaha A 500 Integrated Amp and Speakers

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.  

Details are below:

Is it safe to use this amp with these speakers or should I shop for an amp specifically rated for 4 ohm speakers?