The most obvious one will be the design. IMO, BX400 has a better design with a basic all black frame compared to EX400's black frame with a grey plastic slapped on the bottom. Looks so cheap. Even the "SONY" word on the BX is made out of metal, not printed like the EX400.

PQ wise, both is the same. Both is using the same speakers as well. However, EX400 has Ambient Sensor and BX doesn't have. BX has FM radio function.

In terms of input, BX lacks HDMI ports (only 2) compared with EX400 4. Both has one PC in, USB, one RF, two composite and one component.

If you're already eyeing on Sony, then go get one without hesitation. LG lacks contrast and colour appears to be too pale. Samsung TVs has fake colour reproduction (like water colour) and Panasonic only does good Plasma, but not LCD.

do note that the comparison I typed out is a comparison between the same model across the range. This is already two levels above. Go get it before the stock finish.