IMO, you be better off ditching the HH3 for a simultaneous dual band router if you want to change any piece of the Infinity equipment.
It's rumoured matching cabinets/modems are better as the firmware talks to each other, only rumours though.
I have not seen any difference between the two to be honest i have the Huawei and my neighbour has an ECI
and there is no difference in IP Profile or speed like you posted Ryan it seems like a rumour
FWIW, I have monitored quite a few connections using an ECI DSLAM with an unlocked HG612 modem.
Quite often (not always) the connections were still on fast path after being connected for a few weeks.
Most of them end up having Interleaving applied at a fairly low depth after a couple of days with the HG612 connected & thus sync speeds / IP Profile reduce & ping times increase.
Once monitoring has completed & the ECI modem reconnected, IP Profile, therefore sync speeds, increase again after a week or so.
We can only assume that is beacuse Interleaving etc. has been removed again.
The reverse MAY be true when connecting an ECI modem to a Huawei DSLAM, but as it is so hard to get any meaningful stats from an ECI modem, we just don't know for sure & I'm not aware of many people using ECI modems with Huawei DSLAMS to even get a decent volume of IP Profile data.
So maybe there is SOME truth in the suggestion that modems should be matched with DSLAMS wherever possible.