Not that this makes a big difference in this discussion, but just to get the facts straight:
Yamaha was making some of the top headphones available for the consumer market
as far back as the late 1970's.
And its pedigree as a serious music company is at least as good as Sony's
if not better.
okay, sure. they may have made headphones, but whenever people are throwing out headphone or brand recommendations, I haven't ever heard of Yamaha being recommended until now.
of course, I have not gotten a chance to try the Pro 500 yet. But even just comparing the $300 Pro 400 with the $400 Pro 500, the specs are EXACTLY the same except for the fact that the Pro 500 has aluminium earcups. Sure, the aluminium earcups may positively effect the sound, but in my personal opinion, you shouldn't have to shell out an extra $100 for that. If the Pro 500 was priced at $300, I would say it is a good alternative, but for $400, you are kind of being swindled a bit (in my personal opinion).
However, when you can get the Sony MDR-1R for $300 or less (highly rated comfort, very well-rated sound, original design), I don't see why you should pay an extra $100. Both are made of plastic and metal, so it's not like there is a significant upgrade in materials.
I doubt the Pro 500 sounds "better," just a different sound signature. If you try both and absolutely love/cannot live without the Yamaha sound-sig over Sony, then go for it. just wanted to make sure you knew there are a ton of other highly rated alternatives in this closed portable niche that is $300. more expensive does not always equal better.