It may be that the Spektrum servo's pot is extremely far off from the values the Mini-Z board is looking for, therefore will not work no matter what you try with it. I don't think you fried your servo, but assuming you did everything right and it's not fried, then the servo is just inherently not compatible with the ASF board. Nothing I can do about that.
With the ASF board I highly recommend the Futaba S3113 or S3114, and to a lesser extent the Hitec HS-50 (difficult to solder to). These I've tested to work and respond well, and provide enough space to allow you to run the MRCG in 94MM config.