Frankly, i just searched ebay, and while I didn’t find an “LGB euro sound box” , (well there IS one from UK for $349, very high imho) , i did find a sound stainz, with video link. $169,00. I thought the sound wasnt bad at all (versions vary. Imo told you simply cant tell until you hear the sound, ie ok or sandpaper)
For that price, i suggest you could buy the loco, have decent sound, zero brain damage, and....save $100 over doing a stand alone sound unit of any sort. The price, imho, is very good.
If i wasnt tapped out due to xmas, and more than a few indulgences, , id buy it myself.