For sound, its hard to beat the Massoth XLS sound board (and decoder) combined - but its £160 or thereabouts !
My two diesel loks had analogue sound boards in, which were very good, but the sound would glitch after ten minutes (due to the capacitors I reckon) when married up to two pairs of LGB 55021 decoders.
So I sold the sound boards to two friends here and replaced them with Massoth XLS s.
This is what an analoue sound set up looks like......... (capacitor bank on the left)
Excellent Austrian narrow gauge in North Wales.