Setting aside the pork for the moment, some of your best choices for salmon are a butter lemon sauce of some sort -- perhaps a play on beurre nantais with lemon and capers (been on my brain lately); a horseradish and/or mustard cream with dill; a bechamel based sauce such as a (shrimp) Nantua; and a cool , slightly sweet, creme-fraiche or yogurt based sauce -- again with dill, mustard and/or horseradish.
Like you, I like the salsa ideas too. But, while they contrast with the mushroom-cream sauce for the pork, they don't compliment it. Ask if you really want both on the same plate. Whatever your answer, trust your virtual palate and not mine. I'm not trying to make you into a mini-me, big-you works just fine.
At the end of the day, the best idea is probably to let go of the cream based sauced for the pork and move on to a wine and/or stock based sauce. There's a lot you can do combining one of those with fruit -- Such as a maple/ginger/peach sauce, a port/fig sauce, apple/calvados, etc.
Otherwise you might want to go with fresh lemon for the salmon, and leave it at that.
PS. If it's possible for you, do think about hot smoking the salmon and/or the pork rather than grilling either or both of them. Huge increase in the level of interest, aroma, and tolerance for reheating.
PPS. (Added on a subsequent edit). I just though of a sauce for the salmon which is exactly right, works cold and hot, and compliments your mushroom/cream with the pork. Ravigote. It's a classic sauce, pre-Escoffier, so there are recipes all over the web. It allows a tremendous amount of freedom in terms of what herbs to use, and how you want to place the lemon/vinegar balance. Just an all around good idea for your particular problem. To give you an idea of what it looks like, it's a sort of French pesto with herbs, anchovies, capers, vinegar, lemon and ... well, it allows for a lot of variations.
Don't use Emeril's Creamy Ravigote though, it's really more of a remoulade than a ravigote, and wouldn't go well on the same plate as the mushroom/cream.
Ex owner/operator Predominantly French catering, ex cook at a couple of good joints