I dunno if it has an effect on sound quality, but component life may be affected.
Is there any way to drill an air vent into the rear panel of the unit, near the top? This at least would give a path for the hot air to escape.
Arcam A65+ & CD72T, B&W 602 S3, Grado SR125, QED S.A Biwire, Russ Andrews Classik Powerkords.
Sony KDL-V40A12U, Sony RDR-HXD910 DVDR, Onkyo TX-SR875, B&W MT-30 7.1, QED S.A XT & HDMI-P, Russ Andrews Yello power cables, Russ Andrews 8-way Silencerblock.