My party ( 5 at that time)was equipped with 2 fine arbalests,1 plain arquebus, Hold well arbalest and a fine pistol on Eder. All 5 shooting at Marwald as opening volley gets him pretty chunked.
Worked like a charm. I had to redo the steps about 5 times until I spawned the Gloves of Manipulation ( + Blunting Belt in the trapped chest) . Seems to me that this is the best spot where you can force the game to cough the gloves due to small distance to map entrance and neat place to make the time pass( I did it with the priest Nedmar).