I'd hope the d10 is a LOT better than the pico using an optical input, as the pico doesn't make noise when using an optical input.
That said, I haven't heard the D10, and have heard the pico. The pico dac is an amazing little source, and I'd recommend it whole heartedly to someone who needs a small usb dac. That's what it is, and it's really very good at it. If you need somethign to be an optical or coax dac, or something to be a preamp or headphone amp, it's not the right device. If you don't need anything but a usb dac, you'll be really hard pressed to beat it for the price, or a lot higher.