I believe you'll find a pretty big dropoff from the 3805 to the 4800, based if anything on about 5 years of technology, despite the fact that the 4800 is THX Ultra certified (not Ultra2). See below:
3805 (released 2004)
Dolby Digital Surround EX, Pro Logic IIx decoding with Cinema,Music and Game Modes • dts ES Discrete 6.1 and Matrix 6.1 decoding • dts Neo:6 Stereo to Surround decoding • dts ES 96/24 5.1 decoding for DVD Video • HDCD decoding
-120 watts per channel X 7 channels
-16 Burr-Brown PCM-1791 24 bit, 192 kHz high resolution DACs on all eight channels, in differential configuration
4800 (released, I believe, in 1999):
Dolby Digital 5.1 and Dolby Pro Logic (not II or IIx) decoding entirely in digital domain • DTS 5.1 decoding with DTS ES matrix compatibility • THX Ultra certified, THX Ultra 5.1 and 4.0 post-processing
-125 watts per channel X 5 channels (requires separate amp for surround back channels)
-Real 24 bit, 96 kHz D/A conversion on all channels, featuring premium Analog Devices DACs (8 DAC channels)
Regards,
Rob