I think it's worth saying first that there is a difference between K or temperature, and spectrum.
You can have two 6000k lamps but one can have peaks in the red, blue, and green portions of the spectrum, while the other may not have peaks in the same areas. This will matter to your plants.
For example:
this lamp has it's major peaks in the green and in the blue/violet portion of the spectrum. While this makes certain marine life happy, it will do little for your plants. While
this lamp has it's major peaks in the green, red and blue portions of the spectrum. This is a much better choice for your plants.
I don't believe there is a single filter (gel) that can take a wide spectrum light source, like the halogen lamps on that link, and pick out the portions of the spectrum you are looking for with any real efficiency.
You may be getting to that point where you are spending as much money and work as you would just buying the lamp you need in the first place. Also, the operating cost of the halogen lamps is many times higher than the fluorescent lamps. They use more electrical power per unit of light output, and do not have nearly the life span.
HTH