I use it with impulses all the time. The input level makes a big difference in getting a metal tone.
Setting levels:
strum hard and raise preamp level until orange LED (on Eleven) comes on
Choose an amp
Adjust input level (in Eleven) to get a hotter signal before the pre-amp stage.
set a tone
Check your output level and adjust so you aren't clipping the output.
Insert TL Space and your favorite impulse
Insert an EQ, there's usually 1 or 2 notches in the high-mids that will make it sound more natural.