I can't give you any info on the JVC as I have never heard them. I have owned the Monoprice 8323 for about a year now and I can give you my thoughts on that.
Let me begin this by saying that I am by no meant an audiophile. I'm no expert and I generally make my headphone decisions based on what makes me want to groove with my music more. With that said...
I'll start with durability and comfort. IMHO, I think durability is pretty great for a headphone of this price. They still look like the day I got them more or less. The clamping force is still as it was on day one and the drivers have stood up excellently even after a few accidental "oh shiz too loud!" moments. The problems I have had durability wise are with the hinges and pads. After a few months of heavy use, the lubricant on the hinges begins to dry out and squeezing can occur once in a while. Not enough to really bother unless you are OCD, but its there. Moving on, the pads are pretty crappy. They can be comfortable "kinda" for 2 or 3 months but after that they get hard as a rock and it feels like you have two solid pieces of plastic strapped to your head. That's OK though because one of the best mods you can do to these headphones is to purchase a pair of the Beyerdynamic DT250 velour pad. Holy crapola, COMFORT. The velour pads make it feel like a much more expensive pair of headphones.
As far as sound quality, as I said, I am no expert so don't expect fancy words such as "dark" or "sibilant" but these headphones deliver quite a lot of sound for the money. They may not be the most accurate headphone in the world but boy are they fun. You can strap these on and just jam out to your favorite music with no worries. With the stock pads, the bass can drown out the mids and highs a bit but the velour pads mellow it out and in my opinion gives a slightly more neutral sound signature. I listen to a lot of EDM and urban music along with some indie rock and these headphones are fun for all of it. They are so fun in fact that I'm returning the pair of NVX XPT100's I purchased because they were boring in comparison to my ear. They didnt have the "groove" effect. My favorite part about these headphones has got to be low volume listening. It sounds great all all volumes but its been very difficult in my experience to find headphones that can still sound fun at lower volumes and these are what I've had the best luck with since I generally listen to music at pretty low volumes. To give an idea, I have my volume at 50% most of the time and thats with replaygain enabled on all my music.
Sorry I couldnt offer a more professional point of view but I wanted to stop by and just give you my $0.02 after a year of owner. They are still my go to headphones any time I want to have fun at home. For portable use, I prefer my AKG K81DJs more.
