ehh.. i do not think you can do anything else than using stereo-expantion and send various instruments to specific posistion in the stereo-landscape
Lmms does not support a quadrophonic-scape .. doubt any daw does.. Perhaps someone know one ??
And you are actually talking about surround, not simply that you want to achieve a better surround effect in your songs? LMMS don't support surround as musikBear said. You have to use other software. Audacity can probably put together a surround music file.