I too am experiencing this problem and have been messing around with it for a couple hours.
As it stands I can load EITHER optifine OR the shaders mod. When I try to use both it crashes with no error messages (opens...tries to load...goes back to tekkit launcher).
With Optifine only I get no shaders options (obviously) but it works fine.
With shaders mod it looks like it's super bright like i'm standing on the sun and can only see if i aim straight up at the sky (with SEUS v10 Ultra DOF -- I haven't tested any other) but when I try to disable the shader and return to internal or none the game glitches out and I'm forced to shut down.
I'm still experimenting but if I get the shaders to work with tekkit I'll post back here. Please do the same :-)