It depends on how Roon works with a specific DAC and the capabilities of the DAC.
The 64bit float calculation performed within Roon are basically the same as the processing done in a professional DAW in modern mastering, so don’t worry about that at all. The degredation that can occur depends upon what happens between the internal 64 float pipeline in Roon and the I/O to the DAC. Ideally, when using DSP (for EQ or even volume control), Roon should switch the DAC to its maximum bit depth which would be ideally 32bit (maybe it always does this - I have no idea).
With a 32bit DAC, that would basically mean that Roon can apply up to 96dB of cut and still yield CD quality, assuming also that the dithering algorithm was a professional standard shaped noise algorithm.
With a 24bit DAC, then after about 48dB of cut you will be loosing resolution. If the DAC is left in 16bit mode, than any processing will degrade the signal by raising the noise floor (relative to signal).
Also of course it depends on the gain of your amp. It you have a massively over powered amp, with multiple internal gain stages so that it can output several hundred watts and thus has to always apply a lot of gain reduction before the amp for normal listening, then of course issues may be become apparent far sooner than say with a low power valve power amp for eg. While a pre-amp faces the same problem with an under utilized amp, noise due to insufficient bit depth can be more unpleasant than analog noise depending on how it is shaped.
Best ask the Roon folks how Roon actually behaves. Personally, unless I know how a specific digital end to end pipeline works, I prefer analog control so I can just ignore it.