Took a few minutes to get initial proof of life out of the GTXes.
Here's a PRBS-15 out of the front panel "sync" port. Cable losses de-embedded to the SMPM reference plane, but losses in the DC block and SMA - 2.92mm adapter are not included in the de-embed.
After the PCB channel (about 100mm of TU872SLK), once I spent a few minutes tweaking TX FFE settings, the waveform comfortably passes the XFI eye mask.