Thanks Norman...
Just to let you know Protodrive version has 3 horn choices also and has 26 functions plus 7 more which the user can swap about whereas Dapol fitted chip (which is the same Zimo decoder used by Protodrive) but only has 19 according to their list. I have seen factory fitted speaker installed by a chap on his forum and I did start with the same speaker which is ok, but from cheap end of the market. However I have changed this to a double Zimo speaker and improved quality of sound is very noticable. The speaker is best placed behind the grill to get clear sound, mounting above the motor or in the roof is more muffled.
As far as I'm aware Dapol use DCC Supplies to fit their sound decoders not the factory that made the locos. As I said I did enquire once as I think paying more than the cost of the loco to have sound is just nuts. Especially when it only takes a few minutes to fit and parts and total cost of parts used are half cost at £100. I did not feel I wanted to part with another £100 for fitting cost! They said they did not know if they will provide the Dapol class 08 sound seperatly. I think it highly unlikely that they will as I expect sound files are Dapol property. At least you have he correct decoder and if you want a change, then it can be reblown by any of the other suppliers for a fraction of the cost.