I'd be interested to hear about your experience is when you get your E10 in. I use the PX 100 IIs a lot (currently just being run out of my sound card through an inline volume control), and they sound nice without any amp, so I'd like to know whether you experience a notable sound quality improvement, or if it just lets you drive them louder.
Looking through some responses from FiiO in various threads, it sounds like they lowered the kick-in delay after idling from 0.7s to 0.1s with the newer models, but that the delay is still present, so it all comes down to how sensitive you are to that sort of thing. A 100ms start-up delay wouldn't really impact most music (especially if you have a continuous playlist, where you would only hit the delay on the first song), but it could definitely impact other general sounds coming from your computer, since some notifications/click sounds may only be 100-200ms long themselves.