I recommend your friend watches the available RME tutorial videos:
http://www.tonstudio-forum.de/blog/inde … al-Videos/

Basic principle of operations:
- make sure you enter submix mode
- in control room: assign : phones9/10 to Phones1, phones 11/12 to Phones 2
- click to Phones1 in control room (its there after assgning the analog outputs to Phones1
- now you create a submix for Phones 1
  raise / lower faders of hardware inputs (upper row)
  raise / lower faders for Software Playback (middle row), DAW / Application playback channels
- now click to Phones 2 in control room
- also here you can create a submix for Phones 2

This way you can create submixes for all Hardware Outputs, also for the channels in the control room.

If you want you can save
- output to your main speakers as Snapshot 1
- output to Phones 1 as Snapshot 2
- output to Phones 2 as Snapshot 3
....

And the whole settings you can save then as snapshot and workspace.

As far as I remember you can select snapshots 1..8 from ARC USB.

Then you could this way easily take care, that with the 3 snapshot Buttons on the ARC USB you can listen to each of the 3 destinations as you want.

Thanks for the flowers :-) BTW incredible good job that you do together with your friend !!

A few more tips.

1. Its also very useful after having saved snapshot and workspace to save it all together
    into one of the 30 workspace quick select slots.

From there snapshot and workspace settings can be saved and recalled alltogether.
I think you don't really require it to keep it simple and better handable for you.
But I simply want to mention that this could enable you to
- expand the concept of saving 8 Snapshots for your device
  by having then 30 times the possibilities to store i.e. the 8 snapshot slots of your recording device.
- to make a complete backup or snapshot / workplace settings
  before you try out something new in terms of these settings
  maybe also useful for your friend to know when making all the fine tuning together with you.

2. TotalMix settings: think about using the following TotalMix settings - hit F2 to enter TotalMix Options -> Preferences:
- disable (   )  Snapshots - Do not load Main volume / balance
  purpose: then you have a defined volume when restoring snapshots preventing unexpected high volume
- enable ( x )  Always init DSP devices with TotalMix settings
  purpose: then you do not become asked whether you want to use the newer settings in the device
  or the stored TotalMix settings when booting Windows and logging in newly.
  Then the stored TotalMix settings on the computer will be used and you do not become asked.

> You wrote:
> I know that connecting condenser microphone to unit is dangerous while phantom power is active;
> but there is nothing to do.

I think I have a solution for you: Use different snapshots to have phantom power enabled to Mic 9, 10, 11, 12
Assuming that you will use always headphones to record from Mic:
- restore the snapshot for i.e. Phones1 (could also be Phones 2, whatever you prefer)
  which already has the proper routing and volume settings
- save it to TotalMix SnapShot 4, 5, 6 and 7 without modification
- then recall snapshot 4, enable phantom power for Mic 9,   save it, rename it in TotalMix "Mic09 +48"
- then recall snapshot 5, enable phantom power for Mic 10, save it, rename it in TotalMix "Mic10 +48"
- then recall snapshot 6, enable phantom power for Mic 11, save it, rename it in TotalMix "Mic11 +48"
- then recall snapshot 7, enable phantom power for Mic 12, save it, rename it in TotalMix "Mic12 +48"

By this you can enable phantom power for each of the Mic inputs.
If you use stereo microphony also no problem, then simply take one snapshot to i.e. enable phantom power
for the 1st two Micro Inputs.

Another recommendation is to use Snapshot 8, the last one for "SILENCE" to mute all the Hardware Outputs.
Not only for the currently active Monitor or Phones, simply all outputs.
This is a nice settings where you can be sure everything is Muted, whatever you do.