You may want to take a look at the KLH Model Fives. Their prices are going up but they can be found in your price range needing a cross over rebuild, but well worth it.
These are known for outstanding bass, very nice mids and highs, also non fatigueing. Great for any music. They can take lots of power and set up with at least 8 feet between them will give an outstanding sound stage.
The KHL Model Six and Twenty Three are also great speakers.
Have fun with your search.
Glenn
Sounds like a good idea. The 780 is only like 40 or 45 watts per channel, but what were the old '60's Fives rated? 50wpc or something? I assume the earlier ones are more-sensitive than the later ones, just like with the Wharfies. The Fives might be a better match for that receiver. Depends.
If you spot ANY University models in your price range, grab 'em. Those are underrated and sound very, very-good. High-quality stuff that was priced up there with Altec stuff. Bozak is another possibilty. Boston Acoustics as well.
Some people scoff at cone-tweeters, but my favorite tweeters are the cones in my avatar (alnico Wharfedale Super 3's... same ones used in my W90's). Depends on the speaker though. Most speakers from 1980 or later that use cone-tweeters are not all that good. But a pair of W70's, W70B's or W70C's with some good tube gear powering them can knock your socks off. And the same goes for the even larger W90 and W90C (I believe it was simply called W90 until the W*0C series came out in the mid '60's... No W90B as far as I know). Ultra-smooth, yet airy-sounding highs. Rich, coherent, refined mids (Here's a pair of early W60's from around 1962-'63 with some good tube power, just to give you an idea of the kind of mids I'm talking about:
https://m.youtube.com/#/watch?v=qxPljs82Xgw ). Excellent separation. Plus, they just have the
tone. A truly-authentic-sounding speaker for music from the '70's and earlier (Old blues from the '30's, '40's, '50's, and '60's? ... Forget about it... They OWN that stuff, and the same goes for the old jazz and country too). If classic-rock and '60's and '70's music is your thing, you will surely want to put the W*0 models on your "someday" radar. I will NEVER sell my W90's. They do tend to run in the $300-$500 range nowadays though, as they are the TOTL model in that line (Six drivers... Two 12" woofers, two 5.25" mids, and two 3" tweeters per cab).
But for the Pioneer SX-780, my guess would be to look for the KLH Five, Six, and Twenty Three, plus the Dynaco A25 and A35. I thought about the AR2ax, but they would be harder to find for $200 or less. The Epi (Epicure) 100 is another to look for at that price.