Just to confirm my above post, now I have checked my connection. BV8-40 using L/R RCA from BM5 to L/R RCA BV8-40, VGA. In the connection menu it says AV3, source PC, IR none, HDMI none, YPbPr none, VGA yes, S/P-DIF none.
And it works, seems it automatically finds the audio / sound somehow.
Hope it works!
BV8-40, BV7-32, BL7-1, BS5, BM5, BM1, BL3, BS1, Beocom4