I'm usgin a Harman Kardon AVR80, the only code that does anything on the 15-1994 is 0189 (only the Channel up/down work - as the preset up/down).
I called Tandy for the EFC's and e-mailed them my request... no EFC three days later. Can't wait for them... I just manually went through all 256 EFC's below are my findings. If anyone has similar equipment and can offer more help I would appreciate it. (if this is all the 15-1994 can control on my AVR80 then the 15-1994 is going back to RadioShack)

EFC's for Code 0189 for H/K AVR80 with RS 15-1994
004= OSD on/off (toggle)
017= 7
018= AM/FM Toggle
036= power off/on (toggle)
045= 4
068= mute
073= THX Theatre Mode
077= 5
090= CD
109= 2
141= 3
144= preset scan UP
167= volume UP
169= channel up (same as 144)
172= 8
173= 0
177= same as 169(?)
199= volume down
201= channel down
204= 9
205= 1
208= memo
209= same as 201
237= 6
238= tune/search UP
240= am?
260= same as 004 (260-256=004)