Multiple CEL Codes

[zblack]

Greetings all! I am a very happy owner of a recently acquired 97 Boxster with 95k miles on it. The cars runs great but is producing many CEL codes:

P0134 Oxygen Sensor Ahead of Catalytic Converter (Cyl. 1 - 3) - Interruption of Signal
P1123 Oxygen Sensing Adaptation Area 1 (Cyl. 1 - 3) - Lean Threshold
P1125 Oxygen Sensing Adaptation Area 1 (Cyl. 4 - 6) - Lean Threshold
P0410 Secondary Air Injection System - Signal Implausible (Cyl. 1 - 3)
P1115 Oxygen Sensor Heating 1 After Catalytic Converter - Above Upper Limit

I don't know the maintenance history, so after reading through many posts here I am leaning towards having all four 02 sensors replaced. The P0410 code makes me think there is another issue... I think I will try cleaning the MAF sensor and if it returns, have that replaced, too. Thoughts?

-Zack