Normally adding conditions to a question will be creating a set of "AND" expressions and LimeSurvey uses "scenarios" to use an "OR" conditional expression.

So usually we can create (A and B and C) or (D and E and F)

Now I want to create a condition that looks like this: (A or B or C) and (D or E) and (F or G)

How can I do this directly from "Set Conditions tab" and without going into the relevance equation?

Why not use a relevance equation? After a little experimentation, you will find it much more intuitive and flexible than the conditions editor.