I just tried for random dates mid august.
EK DXB - SEZ (Y) is AED 5k while EK DOH-DXB-SEZ (Y) is AED 3.5k. (Muscat is the same if you decide to do LHR-AUH-MCT) Also, it's an A340. Interestingly though, J is 9.4k vs. 11.4k (more expensive starting DOH).
QR DOH - SEZ (Y) is AED 3.5k while QR DXB-DOH-SEZ (Y) is AED 3.3k so a smaller difference. Also, as I guessed, it's an A319.
As for EY, even though SEZ is on their list of current destinations, I can't find it while trying an online booking.
I would strongly advise that you avoid QR like the plague if you want a 'premium' experience. Either book EK on miles or if paid, start in DOH or MCT based on which connections work better at DXB. Keep in mind though that there's no chauffeur drive at DOH or MCT.