Hi jarome,
Thank you for using the Support Forum. I checked with some people on the issue(s) you seeing and here is what they said:
"Concurrent Ethernet and USB connections are supported for this device. Using a wired and wireless Ethernet connection concurrently is not.
As for the device not being available when in power save mode, this is not a known issue. I would first try adding the printer using a HP Jetdirect port instead of using Bonjour. This solution details how to add an IP printer, for the protocol select HP Jetdirect: http://www.support.xerox.com/go/go.asp?Xlang=en_US&prodID=WC6015&objID=19339&source=DND ".
If the issue continues verify that the device is still online even when it will not print by either pinging the printer or trying to access the CentreWare Internet Services (CWIS). If it is dropping off the network you may also look at the router settings as well. If the issue continues pease consider contacting your support centre for further assistance.