I am not familiar with "I7 15" but will assume it is a speaker. Please correct me if I am wrong. As for the amp setup:
The amp output impedance is not adjustable. The amp is rated at 1 ohm which means you can connect any amount of speakers onto the output as long as the sum total of the load you connect to the amp is not less than 1 ohm
Speaker impedance is also not adjustable but the total load connected to an amp can be altered by altering the way the speakers are connected to the amp.
The formula for calculating impedance looks very complicated but is quite simple.
First you have to understand the difference between series and parallel connections.
Series: Connecting 2 or more speakers by using the negative on one speaker connected to the positive on the next speaker.
Parallel ( // ) : Connecting the positive of a speaker to the positive of the next and the negative of the speaker to the negative of the next.
Connecting speakers in series is handy when you have two 500 watt speakers for instance and want to run them off an 1000 watt amp. Connecting them in series will assure that you dont over power the speaker and damage it. When connecting speakers in series the total of the impedance of the speakers is the impedance of each individual speaker added together. In our example the total impedance will be 2+2+4=8ohm
The parallel connection impedance calculation is a bit more complex.
1/Rtotal = 1/R1 + 1/R2 + 1/R2
1/Rtotal = 1/2 + 1/2 + 1/4
Rtotal = 0.8 ohm
If you have Microsoft Excel installed in your computer you can enter the following formulae as shown into the spreadsheet. After entering the formulae you must enter the values of the speakers into fields A2, B2 and C2 and it will calculate the total impedance for you.
Using less speakers just remove C2 from the formula.
Using more speakers add for instance D2 into the formula
For your specific amp make sure the load you connect is not less than 1 ohm. It is safe to connect more than that but using less will result in the amp protection circuitry to be activated.
If you use one speaker only then there is no adjustment to be made.
Your particular amp can also connect to an additional amp( and speaker) by using the "PASS-THRU" connectors. This saves you from using an additional set of signal wires from the head unit.
I hope that you now have a better understanding of amp wiring.
If you like you can leave a comment with the specs of the speakers you want to use (wattage and impedance) and I will draw up a diagram for you to use when wiring the system.