Hook-up of Stax headphone amplifier

I had to disconnect my equipment recently and foolishly did not take a photo of the various connections.  I have a Stax 40 YO headphone amplifier with 2 sets of rca jacks in the back.  I vaguely recall running one set into my Nak cassette deck (yes, we're old school here).  Not sure about the others.  The manual is in japanese and only shows one set of the jacks being used.  The one thing I do recall is using all 4 jacks.  thanks for your help.