[Radio Wrangler]

Let's rewind back to the beginning.

The speakers supplied with music centres were usually far from the best, and it was a common upgrade at the time to buy it without speakers and get some British made ones instead, from a reputable brand.

8 Ohm speakers in theory won't play quite as loud as the original 4 Ohm ones, from the same amplifier. In reality, speaker efficiency varies quite a lot, and the 8 Ohm ones will not be quite so hard on the amplifier. So the simple theory isn't a reliable guide. 8 Ohms should be fine.

Which would be the best ones to get?

Beats me! they all have advantages and disadvantages. Practically speaking, it's a case of which ones turn up when you start looking.

Size is important. Bigger speakers are less compromised than smaller ones. In general, go for the biggest you can get away with because larger ones not only are better, they are cheaper because they are unfashionable. This tells you a lot about fashion!
Speakers with removable fronts are the best bet, you can remove the grilles and check that the foam or rubber surrounds on the driver cones aren't splitting.

With a bit of care you can get something good for little money. With some luck and a tolerance of larger cabinets, for free is a possibility. Expect to have to collect them. Heavier is also a good sign.

KEF
Goodmans
Wharfedale
Celestion
Monitor Audio
Mission
Bowers and Wilkins aka B&W
Tannoy
Spendor
Rogers
Mordaunt & Short

There are many more British makes worth having. Some are still expensive, but sometimes you come across someone who just wants rid with minimum effort.

These things are fully depreciated. If they are in good order and you don't in the end like them, you can flog them for about what they cost and try again.

Good hunting!

David