Apparently you have some serious voltage problems. Things to look at:
1. Has the Big 3 been done? If not, do it.
2. How big is your factory alternator? Less than 130 amps, need to look at adding a secondary battery or buying a higher output alternator.
3. What is voltage at the battery?
4. What is voltage at the amplifiers?
5. How are your grounds on both amps? Ground down to BARE metal?
6. What size power wire are you using? Also, what size ground wire are you using?
But seems to me that you are getting some serious voltage drop. Causing the t1000 to send a clipped signal to the sub and now causing the 4 channel to go into protect mode due to low voltage. RF t1000 is a current hungry lil fucker. I had the t1500.1bd and had to run two extra batteries due to the current it pulled. At the time I only had a 140amp alternator.