Multichannel PCM is not passed via optical (nor is it passed via coaxial digital). Via optical from your DVD-Audio player for multichannel you are getting either Dolby Digital or dts (of the types available on DVD, not the new formats they have made for BD), both of which are "lossy" (not to be confused with "lousy"; "lossy" means not lossless) formats and inferior to multichannel PCM. You can also get 2 channel PCM (e.g., CD format) via optical, but, again, not multichannel PCM. So it is not a matter of which device is using its convertors. If you want the full sound capability of your DVD-Audio player, and you don't have HDMI (or one of the rare other digital connections that would work with it), you must use multichannel analog connections.
If your receiver is an unreliable brand for HDMI, the next time, I recommend buying a different brand. There is no excuse for that sort of thing being a regular problem with a brand.