Every headphone has it's own sound signature and in the end, it depends on what the listener wants out of a given pair of cans, what sound he/she is looking for, whether or not they like bass/clarity/detail, etc. Personally, I find both to be on the bass heavy side because I usually prefer analytical phones that offer clarity, some bass, and good midrange. My first pair of UE Super.Fi 3s set the reference standard for me and subsequent test drives of various phones have shaped me into wanting different phones for different genres of music. I'll admit I can be a total basshead at times and on part of my collection, it just doesn't do the music experience any justice using a pair of bass-lacking analytical phones and I find I reach for my JVCs. The 8323 gives me another choice so I can almost devote my JVC to jazzier tracks that scream for a laid back sound signature (*makes me melt*).
Don't finalize your judgment (reasoning or emotional) until you've had a chance to listen to a real pair. I've written off other phones in the past based on written impressions and reviews from head-fiers only to go back and revised my own opinions of them when I actually had a chance to test drive them (or buy them). You might end up loving the JVCs, you never know.
Okay, sitting here doing a quick side-by-side comparison. Track is: Let Me Go by Cutline (dubstep). Normal (flat) EQ on my Cowon D2 @ Volume 30. Off the bat, my JVCs are definitely more laid back. The 8323s are more forward and it seems to me have a clearer edge as far as the upper ranges go. So going off of this, the two have different soundstage feel. With the JVCs, everything is more distant, vocals I find are more center stage with bass further in the back and the high hat somewhere between. It's like listening at a grand concert hall. The 8323 is more of a "in your face" feel and that mid-bass...wow. Makes the vocals seem recessed a bit, but I'd put it right behind this bass-centric track. Might be the thump of the mid-bass giving me the impression the trebs are recessed. One thing that does come out with the 8323s that I don't notice (unless I specifically look for it) is the soft whisper of the side vocal/echo vocal near the beginning of the track (as it's building up). On a faster track or a busier track (orchestral comes to mind), I find bass tends to muddle out with the 8323 especially when it comes to bass and timpani rolls and such.
Edit 3: Bad habit of adding in tidbits after I submit, but I digress. I'm loving the feel I get from the 8323 on the Snowy Mountains track off of the Battlefield Bad Company 2 Soundtrack. Some muddiness if you listen in to the timpani roll that leads into a big bass drum thump followed on by more percussion. Listening to the beginning of the track really gives me that airy mountain feel.
Of the two, right now the 8323 offers a much better seal and is a true closed design. My JVCs have lost more of the clamping force over the last few months of at-home use, so the seal isn't the best. On top of that, it being a ported design helps round out bass reproduction, but doesn't lend to a better seal. So something to keep in mind. I haven't brought 8323 on the go with me yet, but the JVCs I have on numerous occassions. High wind here in The Windy City doesn't seem to effect the sound at all (at least I haven't noticed).
The JVCs (I feel) offer better low-end bass that's richer than the bass you find in the 8323s. If you found the 8323's stock pads, small, then I'd say your ears are also on the large side (like mines). In which case, you'll love the JVC HA-RX700s for comfort. I can wear them for 8+ hour sessions and because of their relatively low clamp force, soft pleather pads, and large cups (which go around my ears). I'd also lean on the side that the RX700 has clearer trebs than the 8323s, but I need to burn them in more and with a wider array of music than what I have on my Cowon D2 at the moment.
Overall, yes, they do overlap, but to me, they are each worth the money I paid for them. I gain a foldable portability in the 8323s that I just don't get in the cumbersomely large HARX700s. I also trade off some bass accuracy and a better low-end for the portability and design.
When you get your JVC's, don't be fooled by their size. They are big but quite light, though somewhat heavier than the Monoprice phones.
Edit: Eeesh, I'm starting find this mid-bass thump a bit too much. Drowns out a bit more than I'd like. Anyone else feel like this or just me?
Edit 2: Going off of this review (http://www.head-fi.org/t/608453/monoprice-dj-headphones-8323-review), looks like swapping out the stock cables for some better stuff might improve sound. I never put much stock into how much sound quality can be gained with a better cable, but haven't tried it myself, who am I to judge?
Edit 4: Found some charts/graphs for the Monoprice 8323 if you are interested: http://www.innerfidelity.com/images/Monoprice8323.pdf Thanks goes to TMRaven (found in the review link above).
