I've never heard the P3, but I did own a P5 for a short time. It was feature packed, and relatively inexpensive considering all it had to offer. However, I did not think it sounded very good when compared to other pre-amps I've owned. I did not need most of the "extra" features it provided, so I was only auditioning it for its 2-channel sound quality. I found it lacking, just kind of flat sounding, like a modern HT receiver.
If you are looking for a feature rich pre-amp, the P5 might be a good choice. However, IMHO, if you are looking for high resolution, exciting sound, I would look elsewhere.
Would be happy to hear other opinions to see if they mirror mine.