There are 2 available drop-in boards for the Kato P42:
MRC
1645 - Generic Diesel Sound for Kato P42/E8/E9
Digitrax
SDN144K0A 1 Amp N Scale Mobile Decoder for Kato P42, E8, PA1, F40 and similar locos
The Digitrax has the advantage that if you want to tinker with it, you can download your own sounds to it if you don't like the ones supplied. The downside is that there have been complaints about the motor operation in this series of decoders. Turning on BEMF causes speed problems and possible slowdowns when you use the horn/bell.
The MRC is an older model and there also have been complaints about the motor control - mostly that it's easy to burn up the decoder. Sound is generally considered good though. Also there have been complaints that it's not a true "plug n play" installation. There are small tabs on the top of the frame that have to be removed, permanently modifying the loco.
Other sound decoders will take major frame modifications to make room for the decoder itself, not to mention the speaker system. ESU LokSound V4 micro should fit as should a Soundtraxx micro-tsunami. Both are considered premium sound decoders. The ESU has downloadable sounds, the Soundtraxx is bought with certain sounds loaded.
I have not heard most of these so I cannot rank them, but it gives you something to search on.
John H. Reinhardt
