2005 Mazda RX8 Issues

I picked up this car 10 months ago with only 33,000 miles. Great ride. 3 weeks ago I got a P0420 code according to my reader. It reset but came back on 4 days later. The car then sat for 4 days in the garage and went to take it out and it was turning over by didn't sound like it was firing. Looking up this issue revealed that an O2 sensor was very possible but saw that one condition was cured by disconnecting a negative terminal and another by changing plugs (plugs were all caked). I read that they had to be replaced every 30 months or 37,000 miles. I now have 51,000. I just changed them and did the terminal. Reset code and it still has the same symptoms except now there's a C1306 and a C2776 code. There seems to be a DSC and a Power Steering symbol that I don't recall seeing before??? P0420 isn't there anymore but might to be running for this to return.
Anyone have any ideas?

2005 Mazda RX8 Issues