Powered Subwoofer connected to integrated amp's speaker outs?

I'm interested in purchasing a REL T/7i which is a powered subwoofer. I have an older Marantz PM7000 integrated amplifier which has no explicit subwoofer outs. REL has a tutorial about hooking up their powered subwoofers to the amp from the speaker outs on the amp to the high-level input on the sub. This is all very straightforward and simple. What is not clear, however, is if there will be any power demands on the amp. My guess is no, since the T/7i has its own amplifier. I would like all the power from the PM7000 to be available to the KEF LS50 Metas that I'll have hooked to the other speaker outs. Can someone please address my concerns? Thank you.
The Rel T/7i has a relatively high input impedance so it poses no problem whatsoever. I have an integrated driving Kef LS50s and a Rel T/5i connected to the integrated outputs using the high-level Speakon connector.
Here ya go!!
For those not familiar with REL, they prefer using a high-level connection from your amplifier’s output, accomplishing two things: your main speakers are run full range, making for a more seamless crossover and the sub picks up the exact tonal character of your power amplifier.
I think the REL's "high level" inputs have something like a 100,000 ohm load on the amp providing the signal which seems like none at all...I use 2 RELs (summing the impedance means maybe a 50,000ohm load) running from a relatively low powered (12 to 17 wpc depending on tubes used) little tube amp adding zero strain to the amp, and having no effect on the main (very efficient) speakers. Works swimmingly.
I have tried to use my Rel-like sub using the amp speaker binding posts. Did not notice any real change. It was recommended that I get a Jensen XLR to RCA transformer and run balanced output from my Atma-Sphere preamp the the  single ended input on my sub.
It is said that this is the best connection. Waiting for my Jensen transformer. Look forward to getting better results. I did always think that the high level Rel Speakon connection was best. Maybe not?
Your Marantz PM7000 has summed RCA preamplifier output for a subwoofer.
A simple one male two female RCA block (Y), a pair of inexpensive long RCA interconnects onto a subwoofers L/R RCA inputs would make a basic setup.
You could also add a form of DSP between the Marantz and the sub for far greater flexibility and control than any high level connection or basic crossover and phase adjustments.

When using the REL proprietary high level Neutrik/Speakon connection then simply turning down the gain to hide the subs introduction is instructed.

It’s hardly as seamless as using a low level connection from equalized signal processing preampfification which allows control of frequency and gain to better match the more relevant low level response character of the speakers rather than the amplifier.

Good luck with your choice.

Thanks to all who have replied to my posting! I really appreciate it. It appears that I won't have a problem at all with my desired setup.
Update: I had emailed REL with my concern and this was their response:

The High Level input on all of our subwoofers has an impedance of approximately 150,000 ohms, compared to the 4-8 ohm impedance of most loudspeakers. As a result, when a REL subwoofer is connected using it's High Level input it will not place any additional current load on the amplifier, or draw any amplifier power away from your main loudspeakers.

Their response reiterates what everyone here has mentioned. Again, thanks to all who have replied.