congratulations on your Eclipse and welcome to the forum!
I have owned a number of Boogies in the past, mostly rack preamps, and all of them had their FX loops working at +4dB (line level). I can't confirm YOUR Boogie works the same, but I would be very surprised if it doesn't. The best you can do is to contact Mesa Boogie customer support and ask them what are the Roadstar loop specs.
Enjoy your EVENTIDE !