Not sure what a NAD receiver is but if it can accept an input through RCA and can play, then yes it will work.
I would get the FiiO L7, no point in using the E17's amp as I am guessing the receiver or bookshelves are actively powered.
First you need a FiiO L7
And then you plug it in like so. The L7 works with the E7 and E17.
You plug the L7 into your dock port of the E17 and then you also need a 3.5mm plug like in the picuture. You need a male plug to plug into the L7 and the other end of that wire will need to be whatever the input you want to use is. If your quad amp accepts and you want to use 3.5mm..then do the same. If it accepts RCA then then a male 3.5mm to male RCA plug cable
Now after this is done play some music and go to the E17, are you able to control the volume(and actually hear it get louder or quieter) or use the EQ option of the E17? If so then you need to set the LO switch to the right position. When this happens your E17 is essentially in variable out meaning your pre amp in the E17 is still engaged, some still like to use EQ of E17 or change volume or have or use the pre amp of a DAC or amp combo as it's just what they want but for you, it seems you want fixed line out which means the e17 will be in use just as a DAC. Well like I said above, find the LO bypass switch on the side of your E17...see it? There will be an up or down position. However way you are looking at it. Flip it to the opposite side. It will then be in fixed line out(unless you mistaked the side it was suppose to switch to, try it a few times if not, as the switch isn't perfectly up or down and may confuse you as it's kinda in the middle for some people) This section of the instructions are for only if you are able to control the EQ and volume.
"Welcome to headfi! Sorry about your wallet"
And remember, I do not know what a NAD receiver is, but if it can play audio and will play audio accepted through it's RCA input then it will work.
If you haven't bought an E17 yet, then keep in mind that it looks like this will be a desktop setup, there are cheaper STANDALONE DAC's out on the market that have a better DAC and cheaper than the E17. But the E17 is super multi functional and portable and desktop.
Edited by bowei006 - 7/12/12 at 2:56pm