Staying within the scope of your tiny little window, amplifiers only, crosstalk isn’t hardly even relevant. This would be different of course if there were amplifiers with huge amounts of crosstalk. But that’s the thing. Crosstalk per se is only really relevant or significant when it starts to fall outside a certain range. Which nobody really knows what that is. But that’s the problem with specifications. Nobody really knows.
The thing of it is, if you want to begin to understand the full depth and nature of the misconception here, then think of this: you can get a really solid image from an amplifier with 100% crosstalk. A mono amp. The same exact signal going to both speakers will throw a perfect center image.
Now imagine the same amp only it now has a lot of separation, but still has some crosstalk, and instead of a center image we’re listening to a singer standing ten feet left of center. Everything else with our imaginary amp is absolutely perfect. Everything but the tiny little bit of crosstalk.
So what happens? Almost all the signal is telling us the singer is on the left. Only a tiny little bit is telling us she’s on the right. To the extent that tiny little bit matters it will pull her image a bit to the right. But also at the same time a little bit of the right side is leaking over into the left. Actually the same amount is trying to pull her image each way. So the result is a bit of smearing or loss of focus.
How much crosstalk before this becomes a serious issue? This is where your question is so narrowly focused it almost guaranteed a bad answer. Because phono cartridges have the worst crosstalk numbers in the world, orders of magnitude worse than amplifiers, CD players, just about anything else. Yet my cartridge with its lousy crap crosstalk somehow manages to throw a rock solid palpable wide and deep sound stage that would have you drooling and shaking your head in amazement.
How much crosstalk does my Melody amp have? I don't know. I have no idea. Absolutely none. Its probably in there somewhere. I just can't be bothered with such things. Too irrelevant. I deal with what matters. This ain't it.
Kind of a long way around but that’s how hard it is sometimes to show just how far off base a lot of these conventional wisdom ideas really are. Not your fault. Everyone parrots this stuff so much, so few bother to stop and think things through, its what makes this such a hard thing to do.