I'm just getting back into headphones after a hiatus for a few years, and haven't tried any of the headphones you've mentioned except for the HD650 with a Singlepower 6SN7 amp. Coming from a basic Stax system, the L500 and 353X will be a step up though inevitably I would go for a L700 paired with a SRM-353X. I was also initially thinking along the same lines with the L500 being 1/2 the price of the L700, however after testing, I would not consider the L500. It doesn't offer the value, refined sound and upgrade potential of the L700. I would just mention aside from the lower resolution, the L500 does sit lighter on the head, a non-issue for me. I prefer the ear pads on the L700.