The official CRS paramters can be found here: http://www.mme.gov.na/gsn/nam-map-system.htm.
So it should be Albers Equal Area or LO Gauss conformal. Qgis only offers EPSG 4293 (lat/lon) and EPSG 29333 (UTM 33S). Both do not match with the given example.
You may try one of these: http://spatialreference.org/ref/?search=Schwarzeck
For the local LO 22/17 system EPSG 29377:
The page does not have a proj string, but OGC WKT. I saved it to 29377.prf, and converted the points with gdaltransform from OSGeo4W:
gdaltransform -s_srs 29377.prf -t_srs EPSG:4326 < input.txt > out.txt
Input Y X without minus, and blanks as delimiters. After adding to the Output file a line
E S Z
you can add the file as delimited text layer with blanks as delimiters, marking the E and S column as X and Y. Layer CRS should be set to EPSG:4326.
For LO 22/17, you can test this proj string under settings/custom CRS:
+proj=tmerc +lat_0=-22 +lon_0=17 +k=1 +x_0=0 +y_0=0 +a=6377397.155 +rf=299.1528128 +towgs84=616,97,-251,0,0,0,0 +units=m +no_defs
(Not sure where to bring the "German legal meter" in)
You can add a line with
before your data, and import in Qgis as delimited text with blank as delimiter. Then apply the user-created CRS to that layer.
Comparing both with Bing Aerial map in Qgis Openstreetmap plugin looks as follows. The difference between Solution A and B is about 18 cm. Openstreetmap even knows the place name Ombili ;-)
I think the coordinates should both be negative. "Transverse Marcator - south orientated" should have positive values to the south and west of the reference point (-22/+17). But until someone comes up with a correct projection string, it is easier to swap plus/minus on the input side. This would also apply to the WKT format given at spatialreference.org.