It will be enough for headphones if that's what you are asking. The max I've gone with headphones(HE-500) is a little over half with really well mastered/dynamic material. Compressed recordings I sit at around 9 o clock or even less. I run speakers and headphones just fine without a preamp. Supposedly the csp2+ for instance will add more dynamics. I've tried other preamps but I found it diminished the sound quality due to them just not being great preamps. Decware recommends no preamp as well over a cheapo one. I don't know how good a ca650 is, but yeah just some general advice. My DAC has a little higher output than average, but still less than they recommend on the decware site. Even so I'm extremely happy. 6W is enough for any headphone besides the HE-6 i guess. Apparently even the HE-6 is pretty good with most stuff through the taboo as well. I think you will be very happy with just the amplifier and I'd recommend trying it and getting used to it without a preamp before you add anything to your chain.
Make sure you specify a switch from headphones to speakers, I don't have one and I didn't know you could ask for that option but I'd really like one. I would recommend getting a pair of cheapish speakers even. I'm using 200$ napa acoustic speakers (86db efficient I believe) and they sound really wonderful through the taboo and just enough volume for my bedroom.
From what I've gleaned from the Decware site, adding the switch can be done but it modestly impacts sound quality. Better to use the speaker resistors, methinks.