Right subwoofer for single ended triode amp and high efficiency Altec speakers

I'm sorry, I made a mistake. I tested the terminals when the speakers were still connected to the subwoofer.

I disconnected the cables from the subwoofer, selected the 200 ohm range on the multimeter and got exactly 8 ohm on both speakers' terminals. So the drivers are good.

The question is now: If I get another pair of identical Altec speakers that I have just found online, could I connect them in parallel and drive them with a single ended tube amp without damaging it?

The nominal impedance is therefore 8 ohm and minimum impedance is advertised as 6 ohm. If I connect the two couple of speakers in parallel would I have 4 ohm nominal and 3 ohm minimum? My tube amp has got 4 and 8 ohm taps. Could I drive them properly through the 4 ohm tap?

Thanks