Mutual-Information Maximizing Finite-Alphabet (MIM-FA) decoders have been introduced as an approach to reduce the decoding complexity of Low Density Parity Check codes while maintaining performance close to that of Floating-Point (FP) Belief-Propagation (BP) decoders. The applicability of these low-complexity decoders to practically relevant systems with higher-order modulated signals transmitted over multicarrier systems like Orthogonal Frequency Division Multiplexing (OFDM) is crucial for their application in 5G and 6G systems. We propose a pragmatic approach for the design of a receiver structure for a MIM-FA decoders that can deal with the varying reliabilities of OFDM subcarriers and being agnostic to the modulation scheme. The simulation results indicate that the proposed scheme in combination with a 3-bit MIM-FA decoder exploits the full frequency diversity and performs close to FP-BP decoder.