I’m afraid the best way to solve this means buying a NUC to run the Roon Core. This will be much cheaper than purchasing a new NAS.
I bought mine a while ago, so don’t know the current cost of doing this. Of course it also adds an additional box to the system, but in the longer term it would be beneficial.
There’s a recent thread here that looks at cheap alternatives to NUCs even: Ryzen 3 MOCK Build - it lives!