The solari crystal is LS only, but unlike the qixoni, it is found only randomly, meaning you could play many times without getting it.
But you can use the qixoni even if you're LS. You just need the <FullName> crystal from the Kinrath cave on Dantooine. It is whatever alignment you are if you let Kreia 'adjust' it, so it is LS if you're LS. And if you put a LS only crystal in a lightsaber along with a DS only crystal, their alignment restrictions will neutralize each other and you can use the saber, even if you're LS.
but do you get the benefits of both then personal LS crystal and the Qixoni one?