Buddy,
From the panel, go down the side wall common with the stairs, not behind the toilet. The space above the W/D (behind the electrical panel) is a huge void space with wires running down the side wall and into the ceiling (acually everwhere). I think if you take the screws out of the panel and pull it out of the wall, you'll see what I mean.
Down below, the wall is open to the area under the stairs, accessible by removing the wood return air grille.
Brad
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