I'm new to this forum. could somebody please tell me what the difference is between various versions of the model monitor 10's? I have a pair that has two different tweeters one tweeter has stamped on the back M10 and has a black face plate, the other has sl1000 on the back of it it with a silver faceplate. i bought these these on ebay.Can you tell which version of the 10 they are by the serial number? The numbers are 10A 113748 and 10A 113751.I called Polk And ordered what was supposed to be drop in replacements so that i would have matching tweeters ,they sent me rdo 194s so the invoice says but they don't fit the cutouts on the cabinets. Confused!!! Can someone help ? If Polk doesn't know the difference ,who doe's? Thanks for your help!!