Just use the HPS along with 6500K fluoros for the blue component. HPS puts out a lot more photons, and conversion lamps are a poor compromise. I've used 400W conversion lamps and I've never been impressed compared to an actual dedicated MH lamp on an MH ballast.

(Lermer) I don't know what 400w conversion lamps Paul is
talking about, but in my approximately 10 years experience
with Ceramic Metal Halide, they far, far exceed
conventional Metal Halide and far exceed HPS. The GE
ceramic metal halide has a higher output than the Philips.

You could use HPS along with 6500 fluorescents, but that
would be more expensive and use more watts. Of course if
you add 3 x 54 watts, you are using 162 watts more so I
would be very surprised if you didn't get more yield.

If you use 4' fluorescents but your plants are only the
recommended 2' tall, you are wasting a lot of light
(assuming you use the fluorescents in a vertical
orientation as side lights, which is what I recommend.)