OK, I was hoping for a dump of all the SPORT registers and their settings, but I will try to respond given the subset you provided.
It is important to note that in multichannel mode, it is the RFS that controls the framing for both the transmit and receive sides of the logic. The TFS acts as a Transmit Data Valid signal, which is an OUTPUT from the processor and driven during active transmit channels. If you are configuring your MRCS and MTCS registers to enable channels 0-7, you may be experiencing contention on the TFS if that is externally connected in your system to a host that is currently also driving that signal, though I am not sure how that might play into your failure if everything else is correct (which appears to be the case if the assumption is correct that only the bits you indicate in #1 above are set, xCKFE and xSPEN only). Regardless, Table 24-3 in the HRM shows you the acceptable configurations for the SPORT TCR1 and RCR1 registers to support multichannel mode:
http://www.analog.com/static/imported-files/processor_manuals/ADSP-BF54x_hwr_rev1.2.pdf
Can you stop the host from driving the TFS signal or otherwise disconnect it from the SPORT when enabled in multichannel mode? If you confirm the above settings and prevent the host from driving TFS, then please reply with the full register dump so that I can look further.