The best option here would be to converts the .ost backups to .pst,

I once tried KdeTools for OST to PST software and it was quite helpful. The ost2pst software helped you in restoring corrupt all OST data and converts OST to PST file format in just a few minutes along with all items. 

http://ost2pst-converter-free.software.informer.com/

Hope it'll helpful for this suggestion ...!