Signal multiplexing (blending) with a standard Y adapter?

[mindwave_21]

Didn't know if this was the right section, but...
My bassist can't hear himself in the mix for live tracking, and I'd like to get him to hear more of himself while everybody else hears the mixed out with less of him.

Is it possible to use a standard Y adapter that is a signal splitter to do the blending? I have a 1/8 to 2x1/8 signal splitter (radio shack kind that you use to get 2 headphone outs from a single CD player output), a headphone amp, and my bassist's headphone out from his amp. Right now I'm getting not-so-great results

Here's what I'm doing...sorry I have no pics:
1. I connect the single splitter end to headphones (via a female-female 1/8 coupler)
2. I connect one of the 2 1/8 to the bass amp's headphone out (just the bass player).
3. I connect the other end of the 2-way to our firepod (has everybody, including the bass player).

With the headphones in and one of the 2 "inputs" connected, I get a signal, but when I connect both, I only get the bass amp's output. When I turn the headphone amp up, he gets very little of the signal, but it's super distorted.

Is this a gain mismatch, or something else? I'm using shielded stereo audio cables for all of this.

Thanks!