Enclosure recomendation for ono

I am building an ono clone and I am almost finnished. It uses dual power supply's. My question is what is considered best, to have two boxes one with the power supplys and one with the Pre pre RIAS or dual mono block's ?

In normal amplifiers I see that monoblocks are popular but almost all ono clones I have seen uses two boxes one with P/S and one with pre pre RIA. Why is that ?

/// Carl-Fredrik
Phono preamps have what is probably the least enviable job in the whole audio system. They have to multiply the signal signal a minimum of a thousand times, apply RIAA EQ accurately (and in the process lose roughly 20dB of that gain they just fought so hard to achieve) and do it all without being noisy.
Noise? Did someone mention noise?
Ah ha!
The very fact that phono preamps have such high gain means that they are in danger of amplifying any and every stray magnetic field that happens to wander by...like the ones given off by power transformers.
There are any number of possible solutions to the problem. The easiest is to put the power transformer in the same box and hope for the best. The next thing to do is to build a metal wall around the power transformer, partitioning it off in its own little corner. But the best thing to do is to put it in an entirely separate enclosure so that it doesn't influence the circuit at all. While you're at it, go ahead and rectify and filter the rail so that all that gets passed from one box to the other is DC. That way you avoid any problems with AC hum.
For best results, place the box with the transformer in it at some distance from the audio box. Yes, people usually stack them on top of each other because it looks cool, but further away is better in audio terms.
Not that there aren't other things that can cause problems, but that's another story for another day.