Personally, I believe Sony's motivation to produce this more audiophile-oriented DAP is because they need a vehicle to promote their foray into Hi-rez digital downloads:
http://www.head-fi.org/t/680208/sonys-dsd-capable-pha-2-portable-headphone-amp-dac/105#post_9826125
1) So keen are Amazon to sell digital content that they have had developed, and have even subsidised, their Kindle Fire devices. Sony are shrewd (and experienced) enough to know that they need hardware and content to go hand-in-hand if they are to maximise their bottom line.
2) Apple have had truly spectacular success with their iTunes+iDevice marketing model, which has literally changed the entire music, and portable hardware, marketplaces during the past decade.
3) Sony used the PS3 to maximise market penetration of the Blu-ray format. Few people realise that HD-DVD actually had a better chance of success than Blu-ray, in the early stages, by virtue of the fact that disc replication facilities had a much easier (and more economical) upgrade path for their replication machinery to produce HD-DVD than to produce Blu-ray. There were a few technical differences at the user-experience end of the equation, in terms of playback features, but, fundamentally, the biggest single deciding factor between the 2 formats was at the replication end, and on this basis, Blu-ray should have fallen by the wayside and HD-DVD succeeded. But that was not to be, simply because Sony had the enormous market penetration of their gaming platform, which they shrewdly endowed with a Blu-ray drive when they released the PS3. That single factor sealed the success of Blu-ray and the demise of HD-DVD.
Granted, things aren't so tight, or proprietary, in terms of hardware options available to playback Hi-Rez digital audio files, but still, it is obvious to a major player like Sony that they need to really convince audiophiles of the merits of Hi-Rez digital audio, by standing behind their downloads by offering decent hardware with which to play them. Although an increasing number of people play their audio via computer these days, and popularity of standalone FILE playback hi-fi seperates is increasing, there is nonetheless a substantial percentage of digital downloads customers who, thanks to being conditioned by the extremely successful marketing model of Apple's iTunes + iDevice, equate digital downloads with playback on portable devices.
Add all these factors together, and I do not view the F880 and NWZ-ZX1 as devices in themselves - they are (IMO) intended as standard-bearers for Sony's drive towards Hi-Rez music sales. There is vastly more profit to be made from selling this digital content than there is to be made from selling hardware, since (obviously) there is negligible cost-of-production for digital downloads of their enormous back catalogue.