using a 10W in place of a 5W is perfectly OK as you are using a part with a HIGHER rating. The other way 'round is no good - IE - using a 5W in the place of a 10W - the 5W resistor would either get VERY hot or burn out if the load demanded a 10W. So in your current case you can leave the 10W in place forever if you wish.

I am not a fan of the Altek driver board for one very simple reason. The output transistors that you are having problems with right now on your old board are surface mounted devices on the Altek board. Granted, they are upgraded types being MOSFETs but if you have a problem with one of them I would like to see you repair the board - you virtually can't so the board becomes a write-off.

I would stick with the discreet, through hole board you have now and repair it with the correct transistors - these parts are easily available from many suppliers including me.