There's OpenWRT/LEDE for the HH5A available now also.
Regarding the Lantiq CPE chips, the devices have two chips, the VRX268 / VRX288 is the main chip, plus the VRX208 which is described as the analogue front-end and line driver. The VRX208 chip will usually be found near to the RJ11 DSL socket, the VRX268 is the bigger chip in the middle, often under a heat sink.
The TP-Link 9980 firmware update didn't even need to update the Lantiq DSL firmware, all TP-Link needed to do was enable ReTX in the configuration!