So yeah, been seriously considering the Reflection for a while now. Right around a year I guess. Which is pretty much the way I do it. Research the crap out of it, read all the reviews and comments, talk to some owners, let it stew and gel a while, finally call the owner/builder/designer. Just your normal due diligence.
The way the sub out works, you have a choice. The sub out signal is always there, so no matter what you can run the mains full range and subs at the same time. In addition to this there is the option of using the built-in crossover to filter the low end off of the mains. When you do this, because so much of the power is down low it greatly reduces the power load on the amp. If you read up on my posts about how DBA and subs work you will see it is better as far as deep bass is concerned to have full range floor standers continue to get full range signal. In your case however that is more than balanced out by the need to lighten the load on the amp in order to drive those 88dB speakers.
The Blackhawk uses a 6dB per octave high pass filter that can be set at 80Hz or 100Hz. It depends a little on your room and situation but you typically want to avoid running subs higher than 80 in order to avoid being able to localize them. Set at 80, then your Salk will be down 6dB at 40 which means one fourth the amplifier power. The subs will easily pick this up and so this will allow you to run those mains a lot higher volume than you otherwise would. You were already pretty close and with a sub I think you are home free.
Especially since you are already open to new speakers like Tekton. I can say for sure the 20W Blackhawk will drive a pair of Moabs to deliriously high level, and sound the business while doing so!