You can get an adaptor for your iPad that will allow you to power it and connect a USB DAC, I got mine on Amazon and I use an Audioquest Red, which has a mini headphone jack. You can listen directly or get an adaptor that has a headphone jack to 2 RCAs to power your crack, I got mine from Blue Jeans cable, well made and not terribly expensive. IMHO a vast improvement over the iPad's phone jack output
I actually use an iPod touch for the work bench area to drive an amp not a headphone amp and it works really well
Robert Lees