Not sure what those HS4x JVC are..
Did you perhaps mean the XX around ear explosive bass?
Well if those are them, then I will strongly suggest to skip on those. They are very heavy, not very comfortable and really provide nothing but bass. And I don't mean the good quality bass, but rather kind of hollow cheap sounding bass with no real extension towards the subharmonic Frequencies. I think they're more focused at the upper mid bass impact and mids. But they lack so much clarity, detail and resolution. I tried to like them, I really did, because outside that fact, they're actually well built, they are around ear, but they are perforated on the back side... so Sound does leak a bit. They're easily pushed and clearly meant for portable use.. But other than that, I honestly thought that they were just bad sounding. I don't want to bash JVC on this one, but they should have skipped on making this model.
The HAS600... well, kind of a mixed bag. They're fun portable headphones. Definitely comfortable and are collapsible, so they're easy to travel with. For the price they provide a fairly decent sound and are easily pushed on portable devices. They're drivers inside are angled a bit so they provide a different imaging of sound. They have an overall warmer sound signature and a good amount of bass. However, they're not a bass-heavy oriented headphones (I'm not too sure where you got that one from). Those were the pros of them. The cons, well, they're flimsy and could break if you're not too careful. You will need to treat them like they're a $200 pair of headphones. They have the Y shaped cords as opposed to the newer designs of the single sided cord. Also, the cords are very very thin and are easily snapped if you're not careful. As for sound clarity, like many who stated this, I'd say that they sound more or less like the XB500's, less the bass impact and slightly less forward. If you can be careful with them and don't want too much bass in your music, they're actually a good buy for the price.
As for the XB500's. In my opinion, and if you want Basshead headphones, I recommend those hands down. Other than Shure lineup of 440/840/940 and the Grados lineup, the XB500's are a rare example were the company actually produced a product that not only delivers the promise described on the box, but that the overall sound, design, packaging and care shown to making the headphones, not only is it adequate for the asking price, but actually surpasses it by all means. They truly provide a great deal of bass, and this is quality bass. Of course it's boomy and could overwhelming at times.. But if this is what you're looking for and at this price range, then look no more. In fact, they have better bass presence than the entire Monster Beats lineup at a fraction of the price. They actually also provide fairly good detail for the music. The mids could be perceived as a tad recessed, and the highs have sparkle, but they don't really shine. However, the beautiful part about this is that they respond really well to EQing. Knock the bass a tad, level up the midrange a bit and the Highs... and trust me, they will shine. They're actually very smooth sounding and also a bit laid back. Definitely don't have the forward presence of the likes of Monster Studios, but, they actually have better soundstage and resolution of the music. They're also very comfy... Imagine wearing two pillows on your head... And again... BASS!! It does sound like subwoofers in your head..
Now, if you want a bassheavy JVC cans, you should look into the HARX700 and 900s.
Those are more in the 500's alley..
Hope this helped you.
Edited by Shotor102 - 1/9/12 at 1:34am