I've done a little more calculation, finding the following combinations:

Series

function	ideal	resistors	actual
vol+	16690	12K + 4K7	16700
vol-	23610	18K + 5K6	23600
track+	8656	8K2 + 470	8670
track-	12000	12K	12000
front/back	33545	33K + 560	33560
middle	48125	47K + 1K2	48200

Parallel

function	ideal	resistors	actual
source	2077	5K6, 3K3	2076
att	4338	56K, 4K7	4336
back/front	6477	18K, 10K	6429

I have the Gnumeric spreadsheet I used to calculate these if needed.

Note that I have only tested the four functions I needed, and that I've assumed 0% tolerances on the internal resistor and the sense circuit.