Going to echo @msound here: Congrats! I am saving up to get the towers! (currently have Sierra 2's w/RAAL as L/R in 5.1 system).

I would go with a separate amp, IMHO and FWIW. I went from a "high-end" Pioneer integrated receiver to a Marantz Pre/Pro and a D-Sonic amp...from what was probably exaggerated at 135 W/ch to an understated 400 W/ch (into 8 ohms). (FWIW, I was looking into a crowded $/W market at around 200 W/ch, which is probably "enough" power, then stumbled on D-Sonic)

Immediately the dynamics really opened up...it's like the amp doesn't have to "work" to produce those momentary surges in power that occur naturally from the music...the power is just "there". And, I am talking about "reasonable" listening levels...I like music a bit louder sometimes, while my wife (who has much better hearing, mine probably damaged by years in high-SPL environments) sometimes complains about my chosen volume level for 2-ch music as well as 5.1 movies...

I was really happy with my Pioneer integrated amp, but I don't have a lot of experience with equipment...have been seeking the best-for-my-budget for 30+ years, but wow...the difference with "too much power" is ...well, "musical".

So, one more opinion among many, but I would definitely go for the outboard amp, as what you are looking at will most certainly give you "clean" and fully dynamic amplification, better than any integrated receiver.

Whichever path you choose...good luck and enjoy! Your enjoyment is the most important ingredient!