In the heavy-fermion metal YbRh2Si2 a quantum critical point (QCP) has been established by driving a continuous antiferromagnetic (AF) phase transition from TN ˜ 70 mK at B = 0 to TN = 0 via application of a tiny magnetic field Bc (?c) ˜ 60 mT. New results on the Hall coefficient, magnetic Grüneisen ratio and thermoelectric power support the conclusion drawn from earlier studies that this AF QCP coincides with a Kondo-breakdown QCP or Mott transition, selective to the Yb3+ - 4f states. In a recent investigation, (positive and negative) chemical pressure was applied to YbRh2Si2 to explore the evolution of its B-T phase diagram under changes of the unit-cell volume: Clear signatures of the selective Mott transition were observed within the magnetically ordered phase under volume compression (i.e., Co substitution for Rh). Here, the AF QCP appears to be of the conventional (3D SDW) type. Under slight volume expansion (doping with 2.5 at % Ir) the AF instability and the selective Mott transition were found to still coincide at Bc (?c) ˜ 40 mT. For 6 at% Ir doping, however, AF order appears to be largely suppressed (TN < 20 mK), while the Kondo-breakdown QCP remains virtually unchanged. For this composition, a new type of low-T spin-liquid phase shows up in a finite range of magnetic fields. Further ongoing studies concerning the interplay between the AF QCP and the selective Mott transition in this material will also be briefly mentioned. In collaboration with: M. Brando, S. Friedemann, P. Gegenwart, C. Geibel, S. Hartmann, S. Kirchner, C. Krellner, M. Nicklas, N. Oeschler, Q. Si, O. Stockert, Y. Tokiwa, T. Westerkamp and S. Wirth.