Been listening to the K702.65 a lot over the past couple of weeks -- still on my Yamaha receiver. The more I listen, the more I like.
Personally, I had always admired the bass of the K701. What it lacked it quantity, it seemed to make up for with quality and dynamics -- very tight and controlled, with crisp attack and decay and a solid punch. With the K702.65, AKG seems to have managed to up the ante, maintaining the bass quality and dynamics of the K701 but increasing the quantity to a level that I would call just above of neutral. Definitely adds some fun factor to these headphones without making them sound overly colored in any way.
The mids are nice and forward in the mix, open and transparent and grain-free. The treble is also very nice and clean, with good quantity, but I still think the K701 had a bit more sparkle if memory serves. I was afraid I'd miss the K701's sparkle, but it turns out that I really don't.
If there's one "flaw" for me with these headphones, it would be that I still think they're a bit forward in the upper mids / lower treble region (like the K701, but probably not as prominent). This can make some rock music sound a bit strident. It's still listenable with rock music, but it gets a little fatiguing to me after a while. At that point, it's time to switch to a different genre of music!
Comparing the K702.65 to my current reference, the DT880/600, I would say that the K702.65 has somewhat stronger bass with better dynamics. The K702.65 also has more prominent mids -- I'd say the two headphones straddle the neutral mark in this regard, with the K702.65's mids a little more forward than neutral, and the DT880's a little less than neutral. In terms of treble, the K702.65 is more prominent in the low treble region, whereas the DT880 is more prominent in the mid to upper treble area. The best way I can describe it is that the K702.65 is louder in what I would call the "glare" region, and the DT880 is louder in the "sibilance" region. Both can be a little bit fatiguing in their own regard, but I think which one is more tolerable is entirely up to the listener. Personally, I'm more sensitive to the "glare" frequencies than the "sibilance" frequencies, so I find the DT880 a little bit easier to listen to.
If I were asked to recommend a headphone in the sub-$500 range, the K702.65 and DT880/600 would be my definitive recommendations. However, neither is perfect. When someone makes a headphone with the comfort of the HD800, bass of the K702.65, mids and treble of the R10, and spatial characteristics of the T1, let me know...
I just recently ordered a solid state headphone amp for the K702.65...looking forward to hearing what these headphones can do with proper amplification!