vintage yamaha versus sony amps or ?

Music enjoyment is not complicated. If you like old music - buy vintage equipment,if you like the new sound - buy modern electronic.
Sound engineering and music creation are different every generation and needed to be matched of the engineer and artist intended.

Its even less complicated than that. Most good quality gear old or new makes good music old or new if mixed matched and set up right. Just like most cars are capable of getting you from point a to point b in the expected amount of time. What more is needed beyond that largely comes down to personal preferences wants and needs.

I would only add that technology has improved over the years and that there are more ways than ever to make really good sounding music with more modern gear, especially when the source is digital.

My thinking would be to purchase a used quality integrated amplifier and a USB DAC. What is your budget? Do you currently have speakers or will you be looking for those as well?

bought a SAE 2401 AMP, Sony 77ESD preamp, Yamaha CS300 cd player with BurBrown decoder and my speakers are Polk Audio Monitor 75 T.
What would you change? budget is 1200 dollars.