Any suggestions for connecting . . .

I would suggest that you buy a USB DAC, which need not be particularly expensive if it’s just for casual listening via Spotify, and run it from the USB output of your computer to a spare input on the preamp. For starters, maybe an Audioquest Dragonfly if you want something small and inexpensive. 

You could go straight from the headphone jack but better by far to try something like an Audioquest Dragonfly which offers much improved audio.  The Dragonfly black is cheap and excellent.  The Red a little more expensive but supposedly better still. It plugs into the USB port on your laptop.  You then connect to your NAC82 via a 3.5mm to DIN interconnect.  It's great with headphones too.

Well spotted Richard, I was thinking, but failed to mention, that the Dragonfly will likely improve the sound from your headphones too. 

Piling on with the suggestion of the Dragonfly.  Either model (Black is $100, Red is $200) will sound so much better than the system you propose going into a NAC 82.  If you use the laptop as you propose, you're relying on the dac build into it, which is NOT designed for quality music reproduction. Full stop.  $200 is WELL worth it (and I've read that the RED is far superior to the BLACK).

I have a red and can confirm it is far superior to the black. I use one on my phone too - not only far better than internal DAC, but can drive the headphones to much higher levels (perhaps more useful with a phone) and drive higher impedance and lower sensitivity  ‘phones better.

Try an Audioquest Jitterbug with it (about £40 UK, $40 US) which can make big improvements - it filters  a lot of the mush from the laptop from the USB line adding to the sound (have a look at the AQ website - there’s real electronic theory behind it)

Tried Dragonfly, thought it better than not having one,  but not as good as larger DACs. Didn't quite produce the quality I was looking for.

I recently purchased a black Dragonfly and it really opened up Tidal Master recordings on my 272, from the MacBook, addressing a minor annoyance that I can’t listen to them unassisted on the 272. It also breathed new life into a pair of old HD414s straight out of the MacBook. I actually bought it to drive Tidal masters out of my old Squeezebox Touch but I haven’t been able to get the software to play nicely but I still see it as a great little device with more than one use, even if it doesn’t do it for you in the Naim context. Next stop for me is to get an adapter to try it out in the car.....

It all depends on cost something like a usb dac can cost a few pounds or many thousands but you will need something to clean the signal up if you want to use your MacBook as a digital source for Spotify and iRadio but as a starting point I would go with ALLEYCATS's suggestion of a Google Chromecast Audio for £30 it is unbeatable and if at a later date you want to improve the sound you can add a dac.

If you love your Naim kit, and want to use Spotify, the discontinued ND5XS is an attractive option.  

Nick

Many thanks for all the suggestions. I hadn't thought about a USB connection and did some research and asked around friends. I ended up with a FiiO E10K Olympus 2 USB DAC Headphone amp which had an excellent review on the audio science review web site. I'm very pleased with it; from a logistics point of view its USB cable is long enough to sit on the floor stand of my laptop table and the cable from the amp runs across the floor, so it can be left permanently in place. Oh, it sounds pretty good too!