Pioneer’s BDP-HD1 and Sony’s BDP-S1 can play the same DVD formats (see the list in the Sony BDP-S1 review) though, according to a Pioneer spokesperson, the BDP-HD1 also plays BD-R/RE recordable discs, something Sony’s player currently cannot.
Audio format playback capabilities are identical as well, meaning the Pioneer, like the Sony, will not play CDs. However, while Pioneer’s manual clearly states that the BDP-HD plays back DTS’s lossless DTS-HD format as standard compressed DTS, and does likewise with Dolby TruHD and Dolby Digital Plus (playing them back as compressed Dolby Digital), Sony’s BDP-S1 manual woefully fails to say so.
And here is a quote about the whole issue from Sony themselves...
“At this early stage of Blu-ray player development there are only very few technology suppliers capable of offering components that could be used in the construction of the BDP-S1. It stands to reason that we have sourced key components from similar vendors, however, the design and development of the BDP-S1 was done by Sony.”