7f33ac1a_ecp_cc__Value_Notes
[Part] R4L, R4R [Size/#] 1/8W [Value/Notes] 
These resistors set the input impedance to the buffer stage. High is good -- something in the 100K to 500K range is probably good, and what you pick will influence your choice for C1L and C1R.
ecp.cc
Value/Notes