I suspect that HDMI splitter won't work in your case (but I'm not sure). When using a single HDMI output, the source equipment (your 3D player) will negotiate with all the downstream equipment (your 3DTV and AMP) to determine a signal format that is compatible with ALL the downstream equipment. Since your AMP does not support 3D, I suspect that the player will conclude that the "connected" equipment is not 3D compatible so it will only output 2D video (together with the HD audio bitstream) in its HDMI output.
Zappiti Pro 4K HDR Media Player
Pioneer UDP-LX500
Pioneer SC-LX901
JVC DLA-N5
JL Audio E110
PS Audio Power Plant P10