Power gain is probably going to a bigger front pipe, or something else.
I paid $250 for my front pipe (off fatz), money well spent .
Scotty, I think you mixed up something from that video, the first two 'runs' were inside the car, the other two were outside/sound sourced elsewhere (so went HKS inside -> MINE'S inside -> HKS outside -> MINE'S outside). The sound difference (in that video) between the HKS and MINE'S front pipes is pretty small IMO. MINE's one gives a bit more 'bark'.
fatz had that HKS twin exhaust on his car, there might be some videos floating around somewhere.