You can press after that Shift+up/dn arrow to increase/decrease wolume of whole instrument. And regarding values under envelope first row is kind of accent (0 - none, 1 - fexed value, 2 - never used so dn't know, 3 - value with note-offset), second and third is its value, and the lowest is distortion (warning - REAL POKEY distortions, not RMT ones).
OK, parameters value (from highest one):
- D208 (AUDCTL value)
- time to fade-out (in frames) - for longer instruments
- instrument portamento (+/-) value
- arpeggio (00-7f) or vibrato (80-FF) speed
- four lowest ones - arpeggio/vibrato depth
Also, to have synth with offset, here's value to play with (last one - here's "0c" so higher row can be also tampered ).