The inverse QR (IQRD) recursive least-squares (RLS) algorithm (IQRD-RLS) is very popular because it has good numerical stability and can be mapped onto COordinate Rotation DIgital Computer (CORDIC) processor-based systolic arrays, which are suitable for very large-scale integrated circuits (VLSI) architecture and real-time applications. In this paper, the blind optimal minimum output energy (MOE) detector which is developed for multiuser detection (MUD) in direct-sequence code-division multiple-access (DS-CDMA) systems is implemented using the linearly constrained IQRD-RLS algorithm. Specifically, the max/min approach is combined with subspace tracking for producing the optimal MOE multiuser detector. A new fast subspace tracking algorithm based on Lagrange multiplier methodology and the IQRD-RLS algorithm is developed. A comparative analysis among the recently emerged channel-estimation techniques is conducted using the IQRD-RLS algorithm. The corresponding robust MOE receivers at low SNR are implemented using the IQRD method, and their performances are assessed in terms of SINR, BER, and computational complexity. A robust multiuser receiver is developed by adding a quadratic inequality constraint to the optimal max/min MOE detector. The feasibility of systolic array implementation of the IQRD-based optimal MOE detector is explored. Several simulation experiments are conducted in a severe near-far environment to analyze the IQRD-based receivers and the subspace tracking algorithms.