Why do some CDP's play louder?

I do have two CDP's (one Shanling CD-T100/one Marantz SA 8260). The Marantz plays much louder than the Shanling (through the same Integrated amp). How come?
Thank you for your feedback!
This may be way off, but does the Shanling have fixed and variable outputs? Sometimes volumes are lower on many CD models when using the variable outputs.
its got to do with the voltage output... I believe the current standard is 1.1 to 1.5 volt? However, many of the more mainstream and even higher end units might give you 1.8 to 2.5 volts.. Your marantz might be 2 volt which was not that uncommon. Shanling is probably attacking a little higher end Amplifier market and more efficient systems, for example I have a 101 db speaker and it would get a little annoying not being able to turn up my system with the wrong digital glare occuring with a high output player, and then not being able to put up the preamp to get some of the sweetness out of the pre, the CD then becomes too forward sounding if its too high of output.
Did it ever occur to you to check both players output impedences?
diffrent output gain on CDP's can fool some upon A-B testing that the louder one is better....not so.
Output impedance for both the Shanling and the Marantz is 2.2V
I've had the same experience with 2 different preamps, a Krell KBL and a CJ 12. With the Krell I could get the volume to 1 or 2 o'clock on the volume and the CJ only let me get to 10 o'clock. It did turn out to be system synergy between output and input sensitivity between the player, a Sony 9000ES and the pres and the amp. The amp is a Bedini 801 modified that the person I got it from had some EVS attenuators that solved the problem. A good lesson learned by me on matching your equipment through research before you buy.

Excellent answer, Boss302!