The V3 monos have been sounding great drivng my Klipsch Forter IV and if it had been out at the time I bought them, I would have bought Wiim VIbelink to match my Wiim Ultra.
If you want to use the Fosi X5 with Vibelink, you will use the Vibelink's volume control. You will need to set the Ultra to fixed level output. If you want remote control volume, then connect the X5 to the LINE IN on the Ultra.