Don't the MRC boards lack a decent volume? Has this been corrected?
I've been more satisfied with Williams Alco or EMD boards. I've used them on both a Williams and a Weaver engine.
What I've used for a speaker is: 89-6040 Original New Samsung 45G01BFA 1.875-Inch 8 Ohm 2 Watt Mini Speaker on the bay
It has a great base sound especially when baffled. I was able to use the center of a toilet paper roll (oh my god-where do I find that!?). I then covered the cut down TP center with some cardstock. Great sound.
Easy connect to track power. On the Williams I just plug it in to the boards sound pins.
Alan