Well, having the motivation to change your habits is a great start, so good for you! I think what will work best is a gradual change. If you are drinking 6 cans/day now, try cutting one back & replacing with water. (I like to start the day with an 8oz glass of water with my morning medication/vitamins). Go for plain water, fresh out of the tap (or filtered if you prefer), not flavored. In your mind, picture healthy, fresh, refreshing, wet, thirst-quenching... put positive adjectives in your mind.
Do this for 3-4 days, or even a week, then think of another time that you can substitute a glass of water for a can of pop. Maybe during an afternoon snack - treat yourself to a cold iced tea (unsweetened, you don't want to exchange one habit for another). Or a cup of herbal tea at night to unwind, something you can look forward to.
I would say "no" to the soda stream - if you are trying to cut back/eliminate pop altogether, you don't want to have a device that makes it convenient to drink. Ration out your cans - set them out for the day, & what you have is what you get. Start with the 5 cans, then work your way down. Take as long as you need to be ready to eliminate the next can from your daily intake, but don't let yourself go up. So if that means you go from 6 cans to 5 cans, & stay there for a month, that's OK! Congratulate yourself on reducing your pop intake by over 15%!! Then when you are ready, take then next step.
There are a few things to be aware of that you will need to find ways to overcome - 1. caffeine 2. the enjoyment of the carbonation 3. the sugar - you will crave it & find other things less satisfying until you have reached a pivot point where you find enjoyment from other beverages
Because of the caffeine, I would take it slow on reducing, no more than 1 can/day reduction once a week - so it might take you 6 weeks to wean off pop, but you won't have the withdrawal headaches. To overcome the carbonation, you can try drinking seltzer water (Lacroix is a brand my sister drinks) but it is NOT sweet, so may not be as satisfying. This is where finding positive adjectives for what you are switching to will help - the power of positive thinking. The sugar can be overcome by eating something alternatively sweet, such as an orange or apple - natural sweetness.
On a personal note - I also worked to eliminate pop from my diet, & one of the more difficult areas was when I was out to eat, especially convenience food. When McDonalds says you can get a large pop for $1, with unlimited refills, it almost makes you feel like you SHOULD drink it, because it's such a bargain. So I tried to eat at different places that offered other options, such as Panera, where they had SoBe fruit drinks at the fountain, or where I was comfortable ordering just water (Some sit-down restaurants, like Olive Garden, charge $2.50 for the drink! A few times of drinking water instead, & I can treat myself to a new book). So really think through what other times you turn to pop for your beverage, & what you can do to avoid that temptation.
Good luck, you can do it!! T. :)