JazzmanYou dont need a Digital to Analog Converter(DAC)to hook a iPod/phone up to an amp. The ipod is already out-putting analog signal via the 3.5mm jack. All you need is a aux to rca cable.
JazzmanYou could connect iphone/ipad headphone output to darkvoice rca input, but that's considered double-amping
http://www.head-fi.org/t/726659/double-amping
it might introduce a noise or clipping issue to an overall sound quality.
the reason external dac better,with camera kit, connecting usb to external dac,is that it will bypass all the together the dac and headphone amp inside your iphone/iPad, creating a cleaner signal and no double-amped signal