Landsat8 DN to TOA Reflectance (minus values)

One flaw in your approach. You don't need to go through DN to radiance.
You can go straight to the DN to reflectance.
Just stick to ((B1*0.00002)-0.1)/0.74457226676389733207607359928648.

Here's a good read on the physics of atmospheric correction, and might help with the issue... I'm a button pushing guy, I feel your pain, at least you can just click that beautiful QUAC or FLAASH button once you're outside of academia.

http://modis.gsfc.nasa.gov/data/atbd/atbd_mod08.pdf