Revisiting Radium (v5.9.33) evaluation and discovered this "problem":
When pressing the Vol Up / Vol Down buttons on my PC keyboard, Radium's "System Out" volume changes by +/- 7.5 db.
After 10 keypresses, Radium is at full volume, yet the PC master volume is only at "20 / 100".
It is unintuitive as to why Radium's output starts distorting by simply pressing the VOL UP on my PC keyboard :/
Can I humbly suggest you update Radium to either:
A. Follow the PC master volume scaling and make the db change the much smaller per key press (i.e. +/- 1.4 db per press, so it takes 50 key presses to swing from -35db to 35db)
OR
B. Ignore Vol Up / Down keystrokes all together...
I have posted a gif demonstrating the bug:

Thank you for your time,.