[ 43.286060] cdc_acm 1-1.2:1.0: ttyACM0: USB ACM device
=> Your key is recognized.
2016-01-25 21:27:22.486 Error, ERROR: Cannot open serial port /dev/ttyACM0. Error code 2
=> For me this is fixed after a reboot of my synology nas.
Do not install extra usb drivers or anything, just use the pulsestation package.
Also: do not yet update to DSM 6.
no extra driver and no update dsm 6