Metallic altermagnets remain rare, particularly in low-symmetry three-dimensional crystals where spin-split electronic bands and chiral magnon excitations can coexist. We report a family of metallic d_yz-wave altermagnets in the orthorhombic ternary borides XCoB₂ (X = Ta, Zr, Hf), which crystallize in the centrosymmetric Pnma structure with G-type collinear magnetic order. Symmetry analysis within the magnetic space group Pnm'a' (BNS No. 62.447) predicts a nonrelativistic spin splitting proportional to k_yk_z, with symmetry-enforced degeneracy on the k_y and k_z nodal planes, consistent with first-principles calculations. On the kₓ=0 plane, the momentum-averaged spin splitting reaches 88.4, 52.3, and 70.6 meV at the Fermi level in TaCoB₂, ZrCoB₂, and HfCoB₂, respectively, with maxima exceeding 200 meV in all three compounds. Exchange analysis shows that the altermagnetic magnon splitting originates from symmetry-inequivalent sixth-neighbour inter-sublattice interactions. The chirality splitting reaches 1.51, 2.03, and 3.10 meV below 50 meV in TaCoB₂, ZrCoB₂, and HfCoB₂, respectively, making it accessible to inelastic neutron scattering. Monte Carlo simulations yield N'eel temperatures of 67±1.1, 330±5.7, and 307±5.0~K, placing ZrCoB₂ and HfCoB*2 above room temperature. With spin-orbit coupling included, all three compounds host symmetry-protected Weyl points near the Fermi level, Fermi-arc surface states and sizable intrinsic anomalous Hall conductivities σ*zx of +342, -392, and -221~S/cm at the Fermi level, reaching maximum magnitudes of 763, 942, and 924~S/cm for TaCoB₂, ZrCoB₂, and HfCoB₂, respectively. XCoB₂ therefore provides a single compensated platform carrying both magnonic and electronic chirality, one in the spin waves and the other in the Berry curvature, without any stray field.