to start me on the home theater journey

Maybe this is the perfect time to get a good Umic-1 calibration mic and start using REW to calibrate speakers. It will be a huge help in the future if you plan to get new speakers or sub and need to know how to position them.

 

I found a DM-A405 for sale and i was wondering if it'd work properly with Audyssey on this model.

Well here is a 409 for sale
Pardon Our Interruption...
and some others, though I don't know about shipping to...Argentina? (The flags by our names are very tiny, hard to see)
The microphones all look similar. If the price is not crazy I would want the correct microphone. But if not, hey, better to use a -405 with Audyssey than no Audyssey at all; my area is loudspeakers not microphones but as a transducer guy I would expect differences more at high frequencies than in the bass.

• Is the -1912 compatible to the Audyssey App? That lets you adjust the curve if not quite to your taste.
• REW and UMIK are great stuff but won't help you run the Audyssey on the -1912

As for the center, 4 ohm is fine. Impedance only matters at maximum volume and most 8 ohm speakers are really 4 ohm these days but receivers don't rate at 4 ohms due to some European heat test or such so nobody wants to rate their speakers as the 4 ohms they really are. And the "ohms" are much more complicated than that anyway. Do your AVR a favor though and get a fan like this
Equipment Cooling - ELECTRONICS COOLING - AV Receiver Fans - AC Infinity