This paper provides exact-form expressions for the average symbol error probability (ASEP) of various digital modulation schemes with maximal ratio combining (MRC) diversity over L independent, not necessarily identically distributed (n.i.d.) eta-mu fading channels. The derived expressions are given in terms of the Lauricella and Appell hypergeometric functions and include several others available in the literature such as those for Nakagami-m and Hoyt. General asymptotic ASEP expressions are also derived for all the considered modulation schemes which provide useful insights regarding the factors affecting the performance of the considered system.