Speaker refinish

This would be a job requiring a very dextrous and skilled craftsperson. Veneer is very thin, there's near zero material to sand out. But somehow, you'd have to have a clean, unsealed, & stainable wood surface if you're going to retouch. You can strip the old finish off, but that has a host of different problems and challenges. Assuming you can get to bare wood, you then have to be able to mix and apply the stain to match. But the stained wood and bare wood are going to oxidize and change colors again and they won't match in the future. In short, leave it alone. It's not cost effective or likely to turn out as nicely finished as you'd hope. However, maple changes color much faster on exposure to light than you might think. I've refinished several maple tables and they all started to turn darker within days of the finishing work when left in a reasonably well lit location that received sunlight.

Just be aware that only oil or wax finished veneer will be affected by what Steveaustin suggests. Most speakers are finished with a catalyzed impermeable finish that no oil or conditioner is ever going to penetrate.

Even if Steveaustin's ProAcs weren't an oil or wax finish, an oil would have penetrated through the sides of the cracked veneer. Veneers with tiny little knots (like some Yews) or burls have a distinct tendency to craze & crack over time. Once the surface is broken with a crack, then oils can get in and do their thing. As Lars says, things like Scots do make wood look pretty. But, it's just a surface film that doesn't penetrate most wood finishes. Furniture polish manufacturers tend to suggest their products can accomplish things that are unlikely, such as nourishing wood. Rather like the implied promises of women's cosmetic moisturizing products :-)