TV-Tuner/Antenna Reception Conundrum

[Dyndrilliac]

First, let's get my hardware out of the way.

Antenna: Click me!
TV Tuner: Lumanate TVT8 Wave NTSC/ATSC External USB2.0 (couldn't find a link for it)

So, I have an ancient (circa 1991 or earlier) LXI analog TV set in my "office". I have my antenna hooked up to a 1i/2o coaxial splitter with one output cable going into the TV and the other going into my external TV Tuner. There are five channels that I'm interested in getting in fairly good quality (my local channels basically, NBC/WB/ABC/FOX/CBS). My TV gets all 5 channels in as good a quality as you could expect from an analog TV hooked up to an indoor antenna. My TV Tuner on the other hand, for some reason appears to only be receiving the last two (FOX and CBS). When I say receiving, I mean FOX and CBS come in perfectly but it claims the signal is so bad for the others that all it produces is a black screen (which is BS, because I have my TV on right now getting the exact same signal and they are all fine). My drivers are up to date, and I am using Windows Media Center (Vista 32-bit) to view the signal.

I have come to the conclusion that the fault has to be with either the tuner or Windows Media Center. Does anyone have any suggestions as to how I might pinpoint which of the two is the cause of my issue, or any solutions?