Basically I want to know if it is a waste for me to buy the SOny MDR-1A given that I have the magni/modi combo? - No. They would work well together.
Should I buy better/different headphones? - In the end its your decision. Just make sure you do your homework first. They also mentioned the AT M50s which have many a good rap. Make sure you've looked at them too. https://www.youtube.com/watch?v=Krdb8lceRoI