I wouldn't try to buy a streamer and a DAC both for $5k. Don't know much about the Gustard but a DAC will make more difference in sound than a streamer. So if you are happy with the sound of the Gustard and just want to clean it up and make it sharper, get an Innuos streamer which is compatible with Roon.
OTOH, if you really want to upgrade your digital performance, Look at chord Hugo TT or possibly a lampizator DAC. then you would have to look at a streamer later. I don't know what you are streaming with (SFP?) but if you don't have any streamer at all, a USBridge Signature or IFI zen will get you 85% of the way there for 10% of the money and that will allow you to enjoy your new DAC.
jerry