Any vintage audio fans out there?!?

I've recently acquired a beautiful Pioneer 1976 (oh yes) SA-7300 integrated amp, and it is awesome... Lord! it's akin to having the mighty Purps with me in my front room...

A couple of questions though...

It has a tone switch, what does this do? to my ears it gives greater sonic clarity... It has the loudness switch as normal and I know about these.

I'd like to add a further pair of speakers, which the amp can carry however, I have some Pioneer floor standers rated at 8ohms, can I add some decent bookshelf speaker rated at 8ohms without sacrificing sonic quality and/or damaging the amp/speakers?!? The reason I ask is on the back of the amp it says 8ohms is fine for one pair but an a-b speaker system needs 4ohms, which I understand to be more demanding... confused!

Any help/advice would be great.

Rock On, but be sensible now.

Kosh

Not sure if this is any help but back to my DJ days of hooking up speakers, two 8 ohm speakers run in parallel (going to one speaker and two wires go to second speaker) would cut it down to 4 ohms. Are the speakers of similar wattage though.
Tone back in the days would bring in or take out a capacitor that would cut the bass or treble. 1973 may be a bit late for that technology as I built switches like that in the late 60's at school.

Yep I think the tone switch may be an early version of what's now known as source direct or something similar - it sounds fantastic either way, but the separation with the normal bass and treble cut with the switch on is something to behold.

On the subject of bi wiring, I don't think I need to do this as the amp has a separate input for the two extra speakers. If you bi wire - into a single input - the ohms will go up in demand... I think... i.e. 8ohm speakers require less amping than a 4ohm pair, I would have thought this amp could easily cope with the extra set without causing any damage... I'm not sure though?!? I'm sure there is a poster out there who understands this fully and it might be that you're spot on.

Cheers...