The K9N series MSI boards are pretty old as alex said (my first PC build was an MSI K9 and I think that was late 2006)
If you are going to replace the motherboard you should really think about this as building a new PC rather than upgrading your old PC. My point is maybe the best reaction isn't simply to run out and get any AMD mainboard that will support 8x processors.
I suggest you take the time and research the whole question more deeply, for example here is a thread discussing the merits of AMD vs Intel/nVidia:
http://www.tomshardware.co.uk/answers/id-1986387/intel-amd-gaming.html
Some people claim that AMD perform just as well as any Intel system, many do not. I personally don't have enough experience with AMD to offer you any advice, however I quote from the above thread:
"I find it very hard to recommend AMD CPU's now, unless you're solely focused on video editing/rendering/encoding and on a very strict budget. The AM3+ socket is essentially a dead-end, it won't be seeing any more updates in the future."
Maybe decide on your budget and post a new thread asking what is best for you money.