More mem, not needed 2 till 4 GB is more than enough for Volumio.
Keep in mind if you’re going to render video, you can’t use Volumio or a low end device, you need more power.
Everything that is working now on the Dell, will remain working.
On the HP, bought 2 from Gé and they replaced the rPi’s. Great piece of hardware. Capable to run JRiver without sweating.