Best bus for multimedial room control

Hi to all,

I'm projecting a system to control the equipment of a multimedial room with 3 projectors, a video matrix and other stuff.

My idea is to build some small button panels with some Arduino nano, a central touch panel with a raspberry and some gateways to the other equipment with some other Arduino nano.

I'm considering to use the ModBus RTU on 485 as a bus between those Arduinos and raspberry, with the raspberry as the master, because it's a simple and cost effective bus to implement, but i want to ask if there's better alternative.

For example a friend of mine showed me the knx (konnex) protocol, that is more reliable and also have the great advantage to not have a master of the bus, because all the equipment on the bus read the data and check if they are interested in the message. In this way, if for example the raspberry doesn't work, the system can still be used from the button pannels, because this buttons send his status directly on the bus and the projector gateways can read that directly.
The problem of the knx bus is the cost... A simple chip that does the conversion between the bus and the uart cost more than an assembled converter for the rs485, and the assembled board for the knx can cost even 4/5 times the rs485 one (and is more difficul to find, while the rs485 one can be bought on Amazon).
Here's an example of board, that also have a library for Arduino already made: Opternus: TP-UART2 Board BTM2-PCB

So, anyone that have build something like that (or something like an home automation) have some suggestions?
Anyone know something like the knx protocol, that work without a master and is simpler to implement with Arduino?

Thanks to all
Cheers
Mix

How do the Arduinos talk to the projectors, video matrix and 'other stuff'. Are you simply switching the mains power on/off?

My ancient laser printer has a WiFi interface, does modern AV gear have something similar?

For example a friend of mine showed me the knx (konnex) protocol, that is more reliable

Who told you that KNX is more reliable than ModBus? I would like to see the reasoning behind this.

if for example the raspberry doesn't work, the system can still be used from the button pannels, because this buttons send his status directly on the bus and the projector gateways can read that directly.

It's not that simple. KNX doesn't support that fallback scenario, but it's true that the system can work without the Raspberry but in that case the Raspberry is useless as all the actions take part without it. It may be a logging facility but it cannot actively change the behavior of the components.
More importantly: KNX is not open. You cannot integrate such a system yourself, you have to buy a very expensive software to program all the components and it's not possible to reprogram a complete system on the fly.

I agree with noiasca that an Ethernet based network is probably best given the desires you posted.

I built my home-automation using ModBus/RS-485 as the base but for me a master/slave architecture was totally OK.