Which of the two, the NAS or the HTPC do you envision expanding? Use the upgradable MB for the box that you see changing the most often.
For most folks the answer is the NAS, more drives, more functions, more memory. The storage you have is never enough.
In my case I have gone thru three different NASes configurations, while upgrading my HTPC once (so it could dual task as a HTPC and DAS client), but this might be different for you.
My two cents, but of course this is the DIY NAS forum, not the DIY HTPC forum. They might disagree.
Your electricity bill may also disagree, HTPC generally don't end up running 7x24, NASes often do (2am rsyncs and other hygiene).
For most folks the answer is the NAS, more drives, more functions, more memory. The storage you have is never enough.
In my case I have gone thru three different NASes configurations, while upgrading my HTPC once (so it could dual task as a HTPC and DAS client), but this might be different for you.
My two cents, but of course this is the DIY NAS forum, not the DIY HTPC forum. They might disagree.
Your electricity bill may also disagree, HTPC generally don't end up running 7x24, NASes often do (2am rsyncs and other hygiene).