I didn't see there is any use of AAC in low bit rate since the support of AAC in Sony Network Walkmans were crippled & incomplete. HE-AAC is without doubt, the best solution for low bit rate audio encode and playback, and is well known for its ability to reproduce decent sound even in extremely low bit rate, namely 48kbps, and in some ABX listening Tests, HE-AAC @ 48kbps scored even higher than some mp3s @ 128kbps. I don't know if there is any possibility to add that support by future firmware updates (if there is any). Even with its low-pass filter on, HE-AAC still sounds better than most MP3s and if SONY has the courage to abandon its beloved Connect Store, SonicStage & Atrac3s, then I bet SONY should have no problem going one step forward towards openness by completing the support for AAC playback. and BTW, WMA8 & 9 is utterly sh*t, however gained a large population and I have no complaint of supporting then in SONY's NWs, but the new WMA10Pro is way better than its predecessors in terms of sound quality, and it sounds marvelously @ high bit rate e.g 192kbps. We will be pleased if SONY pull out its ear-buds and finally listen to us. PS. other outstanding formats like ogg & mp3pro are not on my wishlist since it is unrealistic and nearly impossible for a company like SONY to support them.