Since there aren't specifics about the PIE adaptor here's a small writeup with my experience with installing it on my 2004 navi TSX. I had posted on this thread with a link to the PIE forums asking about using their products on a 2004 TSX. I had also PM'd McNuts who had done an install with a different PIE adaptor. He used the HON03/PC-PIOX and I used the HON03/PO-SON. We both needed the HON03-F/MM y-cable which is the same deal as if you were using the SNHOND3.
You can also get the HON03/PC-PIOX and then get the PIO/P-RCA cable (in addition to the HON03-F/MM) to achieve the same results. 2005 TSX owners with XM may need a different adaptor. The PIE products seems to sell for less than the SNHOND3 adaptors, but look and act the same and seem to be available more.

As for the PIE HON03/PO-SON: This thing is plug & play - unplug the navi from the HU, plug into one side of the HON03-F/MM, then plug the adaptor to the other side and then put the connector into the HU. Simple & painless and it works great with 2 minor issues I don't care about:
1-) The navi voice doesn't work unless the HU is on (either the radio, the CD or the Aux must be on). I don't care because I turned the voice off 5 minutes after buying the TSX. If you really want it, you can turn the radio on and leave the volume at 0, since the navi has its own volume level set through the 'set up' menu. If you have the voice on, and you're playing something from radio, cd or aux, volume will go down and the voice will talk, so this behavior is unaffected by the aux input.
2-) When you switch to the aux input by hitting CD twice, if there's a soruce playing when you switch to the Aux, about 5 seconds after hitting the Aux button, the sound will cut off for about 2 seconds, then come back. After this, the sound is excellent.

I've got a Radio Shack RCA to mini plug cable going from the adaptor and into the CD tray by popping out the light on the CD tray and running the cable through there. The cable is super thick and well shielded with plenty of rubber insulation, so the heat & emi shouldn't be an issue. The only thing sticking out into the CD tray is the mini plug and less than a meter of cable so it's easy to shove the cable back in and close the door and nobody knows you've got an aux input.

 

I have the shond and it still does this... is that normal?