In my experience, it would definetely be a 8th house sun because my Venus is in the 6th house. The 6th house Venus for me is one of the main areas of trouble in my chart. If only it was somewhere else, I could probably find the battles of 8th house sun a lot more manageable!! The two of them combined makes all my effort in career sectors that much harder, because I'm carrying insecurities from my childhood, and then my work life is a struggle too. The Venus 6th for me, has a dominating square, so maybe that's why.
When I said my sex drive is either completely there or non-existent, its because if I'm not feeling emotionally or spiritually intune with someone, then I feel no desire to be with them. Even if the trust has been broken in a previously loving relationship, then I simply cannot connect back with you.
I'm a Aries 8th house sun, and a Pisces 6th house Venus. My Mars is also in Gemini.
In regards to the intimidating aura, the 8th house sun is my only connection to Scorpio. It's not a Pluto-esque intimidation, but an Aries fire one. And it's nicely sweetened up by a libra rising, but I've been described as being both sweet and having an authoritarian personality. The darkness has got to come from the 8th house. I'm a Aries-Taurus cusp, and I know that can be authoritarian.
To compare, my sister is a Gemini 8th house sun, with a Gemini Mars in 8th house also, and she has the moon in Scorpio. Call me biased, but I prefer my more light-hearted personality, whereas she has ulterior motives and will trample over the rights of others. I like to think my moon sag gives me a philosophical approach to problems.