The charts I have seen don´t indicate a bass roll off with the classic when loaded with 32ohms phones. However, from my listening tests I´d say that there is a 2-3db roll off with 16 ohm phones.
I own both A818 and Classic. My current IEMS are TF 10, Se 530 and Sony´s EX 90. Overall I prefer the combination Classic + Se 530 bc the Shures are a bit on the dark side and thus complement the classic very well.
Also, the Classic doesn´t have any hiss despite that the fact that the A818 bests it on most SNR tests, albeit by a small margin. I am going to have to say that the Classic easily destroys any previous ipod sans the 1st gen shuffle. I absolutely hated the adjusted open-airy mids on the 5, 5.5, touch and nano 2+3. These are disgustingly deficient audio machines with massive bass roll off of 7-8! db from 100hz downwards and tuned mids, imho.
The Sony NWZ 818 remains rather true to the source. The frequency response curve is very good with a small "fsb-boost" of 0,5-1db in the bass department. However, there is some constant dsp effect doing its magic creating somewhat of an analog sound. Most people will find that sound signature to be "superior". To me it´s a matter of personal taste and IEM combination. I own the 818 for gym and summer use and really like it a lot. There is some hiss with high sensitivity IEMs but definitely absolutely bearable, leagues better than the rattle snake touch. I can highly recommend both DAPs and suggest you buy both!
Prices are coming down nicely on the NWZ. BTW, the UE-11s JwangSDC will be using are on the warmer, darker side as well.
The ultimate DAP for me would be Classic Sound with iTunes+ Sony Controls, UI, Responsiveness, Drag and Drop facility and full metal enclosure.