I don't think you would want to do that, you can try but a stock HU, doesn't have that much power, that 50x4 is peak, and the rms on most units is around 15-20 max x 4
Your mids and highs will sound very weak. I did this for a short time years ago and the bass overpowered the mids by a very large margin. Do a search on eBay. You can find plenty of 2-channel and 4-channel amps for your mids at cheap prices. X-Over also recommended.