output

[Aaron Zahnd]

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[Mourndark]

If the amp has a line out, then it should be fine to take that straight into the desk without DI. The keyboards you mention I am fairly certain have multiple outputs anyway so you should be able to take one (ideally "mix out") into the desk via DI and another (aux) into the amp.

When you say "buzz" do you mean a power hum? If so, it's probably caused by the desk and amp being on different power circuits but being connected to the DI. Check the ground lift as well.