I have been viewing forum topics for a while but decided to become a member when I finally had something to add.  I hope that this helps someone.

I am learning the violin via the Muller--Rusch string method books with a Cecilio electric violin that I got as a Amazon Warehouse Deal.  I tried to add a electronic metronome signal through the "mike" port but the resulting boom in the head phones was a real problem.  I got creative and found on eBay an inexpensive ($2 including shipment from China) 3.5 mm male ended sterio earplug cord with an integrated volume control.  I can now control the metronome signal to any level I want and it is wonderful.