Yes, angioplasty is compulsary for the diag/om and the rca.. Doesnt sound complicated enough for bypass.. If the lad and cx look decent, you can probably stent.
Disclaimer: Judging by the fact that you werent stented already Im gonna assume they referred for bypass already.. This is standard practice and im not trying to go against that necessarily, i havent seen the angiogram, so your physician will know best on that one.
If you really want to avoid surgery however you can obtain a copy of your study and forward it to another physician for a second opinion. Like i said it really depends on how the lad/ circ looks.