Flux-calibrated spectra of the six members of the z ∼ 2.78 LSS: in the top and central panels, we report the LBT-MODS spectra of the four Chandra sources; whereas, in the bottom panels, we show the VLT-MUSE spectra of the two sources that are not detected in the X-rays. The spectrum of XID 109 was obtained in the previous Chandra J1030 spectroscopic campaign, which we present in Marchesi et al. (2021). We highlighted the expected positions of the main emission lines that fall in the observed spectral range. On top of each one-dimensional spectrum, we report the two-dimensional one.