AVB propogation delay

I am sending AVB audio stream 2Km on single mode fiber.
The stream originates from Biamp Tesira server via Extreme X460G2 and 
terminates at the far end to Extreme X440-8p which then delivers avb 
audio to Lab Gruppen Amplifier. This works fine
I remove the X440-8p and replace with single mode Gigabit Ethernet IEEE 
802.3z 1000BaseTX/1000baseLX/SX converter with transition networks 
L1000i-at 802.at gigabit POE injector. Tesira Server indicates Fault is 
"One or more AVB streams inactive". Extreme shows msrp stream failure 
code "AVB incapable egress port.
The Max peer delay setting in Tesira server is 10000ns, the propogation 
time as indicated in show network clock gptp is 12855ns.
I would like to replace 8 port switch with single media converter.
Why does it work with switch but not media converter?