Can I use a Bluesound Node 2i as a Preamp?

I just recently purchased a Bluesound Node 2i to use with my CXA80 integrated amp. However in future  I’m looking at upgrading to a high end power amplifier. As I’ve had the CXA80 for years I want to try a few different DAC’s etc. So in future I’m looking at buying a high end power amp I can plug some RCA cables into and use some different bits of kit. 
Whilst I was on the phone to the guy from the audio store, whilst purchasing the Node 2i I asked about connecting the Node 2i to an NAD M22 as an example. He warned me not to do that for too long, as I’d need a proper Preamp, he was warning me that the Node 2i is not a Preamp. Fair enough but I am a bit confused, what does a Preamp have that the Node 2i does not? How do you define what a Preamp is then? What is the risk of connecting a Node 2i to a M22 directly via RCA? Or is this just a traditional thing that you need a big preamplifier for a big amplifier? I can’t figure out what the reasoning is. Is this to do with grounding of the preamp? or something else? Any feedback would be appreciated.