Is it not
NAS + NUC/ROCK + UPnP Bridge + ND5XS = Happiness
A QNAP 451 is an Intel® Celeron® 2.41GHz dual-core processor (burst up to 2.58GHz) so it depends do you have the standard 1GB RAM or the
and there are experiences reported here QNAP 251 - does Roon Server work on it?
You may need more RAM and an SSD to host the Roon database.
I agree with @Richard_Robbins that it may be better to get a NUC i3 with 4GB and a SSD to run ROCK, then nothing is being stressed.
Simon.