Anyone got SMB multichannel working on OS6?

Hi,

I have old Ultra 4 Plus with OS6 6.10.8 connected on both 1Gbit ports to 2.5Gbit network switch (no teaming or bond configuration , just two separate adapters with two IP). PC is using a single 2.5Gbit to same switch.

Samba used is version 4.8.0, which should support SMB 3.11 and multi channel (albeit experimental)

I added multi path configuration into smb.conf, configured PC adapter for RSS and verified that network is indeed capable of >1Gbit speed by running two iperf3 sessions on two different ports and IP’s towards NAS (and was able to get >1.7Gbit)

Yet, my SMB file transfers are capped at 1Gbit.

I verified PC SMB configuration in Powershell and it is indeed using two different IP/paths to NAS and using SMB 3.11. But something is throttling in NAS Samba. It is not drives nor CPU. 

Did anyone succeed getting more than 1Gbit on single file transfer session? If yes, can I get your secret sauce?

Worst case, is it possible to install newer Samba (backported to Debian Jessie)?

thanks