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.
A/V: Sony KDL-V40A12U & BDP-S350, BT Vision, Onkyo TX-SR875, B&W MT-30 7.1, QED audio cables, Russ Andrews power cables.
Hi-Fi: Arcam CD72T & A65+, B&W 602S3, Partington stands, Grado SR125, Kimber I/Cs, QED speaker cables, Russ Andrews power cables.