Similar boat here. I adore my M1570's and I also have a set of ATH-R70x that are very good but can't match the soundstage of the M1570. I rarely use either of them for music though I've found both to be exceptional at it. The M1570's have spoiled me and thus far none of the budget hotness you read about on this sub are an upgrade so I've stopped for now.

Your mention of the HD800S has me intrigued, though, and I'm also very interested in the LCD-GX. Though I love the M1570s I've come to appreciate the lighter weight of the R70x. But given that I'm pretty happy right now the cost of an upgrade just doesn't feel justifiable to me.