Rathian armor + is not very effective. Health+50 can be obtained by eating Meat+Meat or Meat+Grain. Fire Res+15 can be obtained by eating a Firedouse berry while on a mission. Earplugs is the only draw to the armor. If you want Earplugs you can use this set which has Sharpness+1 and HG Earplugs. The materials to make this set aren't very difficult to obtain.
If you can't get the Rathian Ruby, take the low rank head and upgrade it. With some gemming you should get Health+50, Fire Res+15 and Earplugs. With a +4 hearing talisman and a one-slotted weapon, you can get HG Earplugs. You could also replace the head with the Skull Mask. With some gemming you should get Health+50, Fire Res+15 and Earplugs.
Demonic Blessing should be gemmed out with Protection/Asylum Jewels as the skill gives a 25% chance of increasing damage taken from attacks by 30%.
Having Earplugs means you are immune to the roars of all monsters except Diablos, Gigginox, Ceadeus, Jhen Mohran, and Alatreon.