1: You lowered the gains to zero and you wonder why the subs dont put out anything??? 2: you have to set your gains correctly since this is a new ohm load. Here's a basic guide to do so properly instead of doing random settings.
How to Adjust Amplifier Gains Using a Digital Multi-Meter | Learning Center | Sonic Electronix
3: Only difference you will hear going from 2 ohms to 8 ohms is significantly less power output and loudness. Lower ohm loads give more power, higher ohm loads restrict power.
4: Your new subs might not even like the current box its in. For bass the enclosure is 70% of your sound quality and loudness despite what most newbs think. There is no hope with a poorly designed pre-built enclosure.
5: Your new subs could be badly engineered subs
6: Some pictures of your setup would really help(mainly what the enclosure looks like and how its sitting in your car) along with proper model numbers of that pyle sub