I'm not sure I'd stick them under your speakers to be honest. Ideally, speakers should be decoupled from their surface with something which holds them firmly, otherwise your bass and imagery will suffer. Though I'm sure contrasting opinions are available. As for your electronics, try both ways and see if there's an audible difference. If there's not, pick the direction which seems the most physically stable. Then there's the question of whether you should use 3 or 4...