flavor30The Fostex T50RP's are known for needing a more powerful amp. The SMSL IDOL will likely sound better than the built in DAC of the Macbook Pro but you might want to consider a dedicated headphone amp to drive the T50RP's or some DAC/AMP combo that puts out in the 400 to 500mw+ range to get the most out of your Fostexs'. The Idol is more in the 100mw range.
flavor30Most dedicated amp/DAC combos are going to be better than the built in ones in laptops. And yes, it will be able to power them. I'm able to power those with my phone, anyways, but almost every set of headphones (except maybe the ma-900) can benefit from an amp.