Jumping stance basically depends on the jump face and area leading up to it , for example a short steep cupped ramp will need some finesse as the cup will compress your suspension , but it can also unload the suspension as you reach the top , which can lead to a endo , or a kick , but generally a neutral position is best to get off the face on a long flat ramp (like a dune) but throttle control goes along with it , if you even slightly let off (with a 4 stroke as opposed to a 2 stroke this is most noticeable and has the most effect) it will not only change the attitude in the air , but it will also most likely lead to a nose dive , so constant throttle input is critical , also you can seat bounce , either slightly or dramatically depending on the jump face and speed , but again , throttle input affects this dramatically .......... with that said , there are plenty more qualified than I am to give you jumping advice , but the main thing is commitment and confidence , short jumping can be just as brutal as over jumping , and always be on the gas just before landing , this will help smoothen/soften the landing , as the suspension will compress much more when off the gas than it will when you are accelerating and forward momentum is displacing the loads on the bike , kind of like skipping a rock across the pond , if it has momentum , it goes a long way , if it is at more of a downwards angle without the forward momentum , it hits the pond and almost stops where it hits and sinks .... follow ??
If you are getting big air , I would recommend keeping the stiffer springs as it will keep you from bottoming on the large hits/landings , downside is as you were experiencing , harshness , so like I mentioned before , there is always a compromise ....you need to decide what is more important , big air , or comfort , as the 2 are complete opposites and are about impossible to get both together , or to set up the bike to do both well , one will be ok or uncomfortable , the other will be great .... that part is up to you ..... you can only do so much , its either comfort or impact resistance ,,, when you watch the pros on a SX or even MX track and you see them hucking huge gaps and landing like a pillow is under their tires , if you got on one of their bikes and rode it , it would be like riding a pogo stick and your teeth would be second guessing whether to remain in your mouth or rattle out taking part of your tongue with them...................... food for thought ..............