I think Nezumi's answer covers whether you could use a one-handed melee weapon and do an off-hand pyschic stab. But it sounds like you're asking whether you can use your melee weapon like a Protoss warp blade, and to that I'd say no. (Although it strikes me that aliens or exsurgents might have some kind of technology for doing this, if as a GM you wanted to introduce it). So no melee weapons, but what of an async with claws, a beak, densiplast gloves, or the like? Can they deliver a psychic stab in combination with a punch or natural weapon attack? The rules say 'no;' touch psi attacks are stated to do no damage. Personally, I think this is very open to house ruling, at least in the case of Psychic Stab. If you feel, as some do, that offensive psi is a bit nerfed, letting the touch attack also do physical damage compensates quite a bit. One other thing I noticed that we should probably fix in the 4th printing: touch psi attacks are stated to require a melee roll. I'm pretty certain we should change this to say it's an unarmed roll instead.