Not sure about this, you should probably try those discs in another PS2 to confirm if this indeed would be the problem. If they boot in a different machine, it's your PS2--if they don't then it's your burner/media not getting along. The A05's have had some wierd things going on with SOME Ritek media. There is in fact a specific firmware for the G03 Ritek's. You might want to check your firmware version. If it's less then 1.30, you should probably look into an update. D/L the media test utilities posted in the sticky up top and make sure your drive is recognizing your media and the correct burn speeds. You may even find you have a different media than you thought you bought sometimes, depending on where you ordered it from. You can get some of the official firmwares as well as some cracked ones (region free, 2X for all media, etc.) for skirting around the media issues here:
Most the guys who work on these are regulars at the rpc1 forums, and you can get some good info there:
If it ain't broke don't try to fix it! But, hell if you can tweak that bastard just a little bit more....hehehe.