Thanks for the quick response. I have tried 2 DLNA server,
a. the netgear R8000's built-in DLNA server which is super primitive and I don't think it has capability to convert m4a to wav before it is served to the Wiim. Same Server serving flac is showing a smaller than 1411 kbps which totally up to my expectations.
b. foobar2000 UPnP, configurated not to decode to wav for m4a and flac, same as above, flac bitrate displayed in Wiim home app < 1411 kbps whileas m4a shown constant 1411 bitrate. In addition, checked the network throughput using windows resource monitor shown the m4a streaming's bitrate is mostly 900 kbps suggesting it is not decoded. Checked the same way to stream uncompressed CD quality WAV shown throughput to be at 1.4Mbps, again all behaved up to my expectation. it is just the Wiim home app display.
Apologies for the long winded reply.