pairing 4 ohm speakers with 8 ohm speakers

You are trying to do too much with too little. Since the
Luxman has pre-out jacks,you should get a separate amp to
drive the rear speakers. Another option is to get an AV
receiver that includes a separate amp for rear channel
operation. Why take the chance and fry your receiver?
Another problem is you will not be able to match the volume of
the front and rear if you use different speakers.

Sorry guys had a family matter to take care of.....My front speakers are in series. I crossed + and - on each speakers so the ohms wouldn't drop.

That's excellent advice to add a 2cd receiver but I'm maxed out of room in the cabinet the components are in. I have a channel selector and turn down the volume to the rears to help this problem.

I crossed + and - on each speakers so the ohms wouldn't drop.

A little confusing. So wire from + on amp to + of one speaker, then - of that speaker to + of 2nd speaker, then - of 2nd speaker to - on amp. Is that how you are wired?

Or do you mean, + and - from amp to one speaker, then + and - crossed to the 2nd speaker? If so, that is parallel with speakers out of phase.

Again, if you haven't tried parallel, you should, sound will be much better. Series wiring for raw drivers is OK, but generally not recommended for speakers with crossovers. It causes a less cohesive sound.

I did it like your first example. I was told this is series. The parallel may sound better but puts more strain on the receiver. I wanted to get away from that for the fact I was running rears.