How well does Sine hold up to other closed portable Headphones such as Focal Classic or even portable headphones below the 499 price?
They are my favorite portables...check my profile to see what I have heard. I will say at a comparable price, it comes down to a sound signature that you most enjoy. I have had more comfortable I have had less comfortable, I have had better isolating I have had worse isolating and so on. It is about finding your happy spot or in my case temporarily as a rule I don't hold on to things long. The Solar are the longest I have had an IEM and the Momentum M2 are the longest I have had a headphone. I switched to the wireless M2 so I have a wireless. I pretty much have kept the M2 as I cycle through others, not that there aren't better, but again they check many boxes for me and now I only use them as my wireless. I focus mostly to find the best portables I can. I don't like to be tethered to a desk. The AK T5p are awesome sounding close cans, but they have caveats. They are not very portable, at least by my criteria and they really shine with an AK source. Those two things and price count them out for many folks. I have interest in the Ether C but they don't meet my portable criteria, but I will probably get them anyway.