Well with any mods there are lots of things to consider. OpAmp upgrades are easy and can make a difference. But also keep in mind power supply requirements and oscillation. The 4558 chip is pretty much universally hated for anything but a Tube Screamer. But it is an inexpensive and forgiving chip.
There are lots of chips that are compatible, from fairly cheap, all the way to esoteric and expensive. Everyone has their tastes depending on their budget. Some also may be pin compatible but oscillate or draw too much power.
Since that board was often compared to Mackie, and I am pretty sure Yamaha's were made by Phonic, I am guessing it is a typical transistor pair followed by OpAmp design. In that case, I had a Pre that I replaced the 4558's with TI NE5532's and it sounds much better. Also the TI Burr Brown OPA2134's are an upgrade and forgiving as well. There are haters of those chips too, but the nicer ones cost considerably more and can have stability issues in certain designs.
Or maybe socket the chips and buy a few to try. Use the one you like the best.
Every chip manufacturer (Analog, TI, JRC/NJR, Linear, National Semi, etc.) all have cross reference matches. You might even be able to get free samples. All the DIY audio guys tend to stick to Analog, TI, and National. But a big chunk of the Prosumer audio gear use JRC4580/5532's.