Parametric average-value models (PAVMs) of line-commutated converters have been developed for efficient simulation of power systems transients. In this letter, the numerical properties of existing current-source (CS) and voltage-source (VS) interfacing techniques of PAVMs are analyzed. A new alternative compensated-voltage-source (CVS) interface is proposed for implementing PAVMs in fixed-time-step simulation environment for offline and/or real-time execution. The CVS approach is shown to have advantageous eigenvalues permitting using larger time-steps while retaining accuracy, which is desirable for real-time simulations of power systems.