Capq, as Kijanki was saying, the DAC1 does upsampling. It uses an asynchronous sample rate converter from Analog Devices so that the data stream that its internal DAC actually sees consists of 110,000 24-bit data samples per second. Redbook CD consists of 44,100 16-bit samples per second. So even though the exact data stream is being delivered by the transport (cheap DVD player), the DAC1 is actually processing (converting to analog) a completely different data stream.
How a 16-bit sample is extended to a 24-bit sample and the number of new samples are created will have an affect on sonics of the DAC. The Cambridge DacMagic uses a different sample rate conversion system (from Anagram Technology) than the DAC1 so it would not be surprising that those devices could sound different.
Plus the digital processing is only part of the problem. The analog section is just as important.
Some high-end transport/DAC systems use a shared clock so they wouldn't require an ASRC to manage jitter.
You might want to read through this for more explanation: http://www.lessloss.com/page.html?id=39&zenid=dtjdphvbk26jqvo4ksr2ki4i37