I'm not shocked that the VGA to component converter didn't work, but I am surprised at the problem you had converting HDMI to DVI. From what I understand, the physical shape is different, but the video information traveling over those two difference cable types is identical. Of course by converting to DVI, you lose sound, but the video content is the same.
I hope mentioning a another company which is not a direct competitor to MP4nation is kosher. If not, I apologize in advance. There's a company called Monoprice which is THE place to go for high-quality, yet shockingly affordable computer, audio and video cables and adapters. I have no relationship with them except as a satisfied customer (just as I am with MP4nation). They have a variety of adapters and cables which could help and are nearly guaranteed to be higher in quality than the ebay stuff you bought.
I just got a 5000HDG and successfully connected it to a HD monitor/TV through the HDMI cable which came with it (an extra accessory). In order to make it work, i had to go into settings on the device and select which type/resolution. On my device, I did this with buttons on the top, but on some devices you may need to have a remote control to access the settings. I'm probably not telling you anything you don't know, but it doesn't hurt to cover all your bases. In my case I think I selected HDMI 720p/60Hz, though 50 also worked.
I hope you can get it to work with your monitor. It's a nice benefit that I didn't have on my last PMP.
The thing is if they both worked for my 360 outputting to my monitor in both hdmi to dvi and the vga converter then theres no reason for them not to be working for my v8000hds other than there are so many compatabilty issues with cables for these dam ainol devices.