Nope. Few things to take into consideration,
When installed an aftermarket stereo on my DS3, similar system to the RCZ, few problems:
If you'll be using the head unit to power the speakers, just an adaptor, as mentioned above. The adaptor will hold most of the functions of the stalk. No problem.
If you'll be using an amplifier, as I assume they'll be connecting using the RCA, the problem is that the RCA just will send the audion, not the bips to the speaker, and will be unable to lower the volume when the parking sensor is active.
Simply, when using and adaptor, without an amplifier in the system, the new head unit will send the audio to the same "route" as the original head unit, so the system still able to control what goes to the speakers.
When using an amplifier, and it's RCA, the new connection will be independent, as the speakers will play what the amplifier sends to them, and the system won't have any control over it, as even using the adaptor mentioned before, the audio won't be using the original "route".
Another option would be using a low-hi converter, using the adaptor mentioned, and after the adaptor, when the cables return to the "route" to the speakers, you route them to the low-hi converter, them send the signal to the amplifier, and from the amplifier back to the speakers.
The easiest plan is just using the adaptor and without further mods, the new head unit will power the speakers.
Including an amplifier, complicates everything, but if it's your plan, I can drop few tips to avoid my mistakes.
Just as a note, most standard speakers will be 2ohm. Using an aftermarket head unit, even with a more powerfull head unit, the standard speakers may sound weaker than before. Worth checking if the RCZ uses 2ohm or 4ohm.
For the RCZ, upgrading speakers was quite easy, just the 6x9 which I canibalized the mounting and used Alpine front and back. No amplifier for my previous RCZ, later using an amplifier for my previous DS3. During the installation of the speakers, some soundproofing and voila.