Several problems that I have with this scenario:
First, it makes no sense that Raf and Amanda had any "time to kill" after the murder if you believe they are responsible. "Kill time" waiting for what? Waiting for the mood to strike to stage the break-in or clean all their fingerprints? They had anything but time, especially since the alleged clean-up wasn't completed by the time police arrived.
Second, I don't believe it's the act of listening to music that's impossible (though I do find it unlikely), but the idea that he decided to create a playlist. If you killed someone and you desperately need some tunes to lull you to sleep you don't spend 40 minutes creating a playlist. You just turn on whatever music you have.
Third, I can't conceive of being in a situation like that where I've just killed someone and my entire train of thought until the police arrived not be about how to fix the situation. Trying to get to sleep or listening to music doesn't add up to me. I think I would be a terrified and frantic mess by the time I spoke to police and I probably wouldn't have gotten one wink of sleep. Amanda and Raf were present in front of police the entire next day, sitting through questioning until the sun went down. If they had committed the crime they would have been up all night and their signs of exhaustion, I think, would have been obvious (especially if we're to believe they spent hours scrubbing the cottage down).
Unless you can provide some evidence to support your contention that murderers never fiddle with their computers the night after committing a murder, this qualifies as a belief (and I would argue an Argument from Incredulity). I happen to believe otherwise. I make no assumption that criminals would never act in a manner that we, as non-criminals, would consider to be non-productive.
Addressing some other points:
1) How often do criminals anticipate every scenario? Is it not possible that it never occurred to them that someone might call the postal police after spotting a couple of cellphones? AK came home, according to her story, to find an open door, blood splattered in the bathroom, and human waste in the toilet. Yet she did not find that of any concern. That is, until the postal police showed up. Then, she was concerned.
2) Is it possible that RS didn't expect to get back to sleep?
3) Can you not think of other reasons why RS would not have gone back to AK's apartment? Such as that they decided that AK would do the cleaning to eliminate the possibility of RS leaving any fingerprints or other evidence in the apartment? Or that having music on his computer was intended to create the impression that they listened to music in his aparrment the night before (RS appears to have not realized that it is possible to determine the times when commands are entered into computer, and he is hardly alone in this). Yes, this is speculation, but so is your contention.
4) I don't find it meaningful to discuss what you think that you would do in that situation. Most criminal acts are committed by people acting irrationally and afterwards they are under a lot of stress. I don't see any reason to expect they would necessarily act in a manner that we, who aren't under this stress, would think would be productive.
As Charlie has pointed out to you there is no evidence to back the claim that they bought bleach.
So you're claiming the report about the receipt isn't true? Whatever. The grocer testified that Amanda shopped for cleaning supplies. I'm sure that it was just by coincidence it happened to be the morning after the murder. And she was in such a hurry that she waiting outside when the store opened. This despite her claim that she had slept until 10. I'm sure that it was also just a coincidence that she forgot about this. Just like it was a coincidence that RS had forgotten that he hadn't used his computer after 9:00 the previous night.
Nope. We know they had access to the inside of the cottage, not to mention this completely undermines the notion that they had been cleaning up to the point the police arrived.
I said RF, not AK, might have not known where AK had the key.