Is an amp the next upgrade path for me? Advice...

Hi all, love the forum, long time fan, and a past purchaser of equipment from here.

My equipment prior to 3 weeks ago, were:
Axiom Audio M22Ti, Arcam a65plus integrated, Axiom EP 125 sub, Squeezebox touch, wiring/power all stock.

Recently purchased a set of PSB Imagine T towers to replace the m22.
Very happy with my decision, soundstage has really opened up!!

Of course, I am now limited to the volume I can play my music (I prefer 2 channel), and have noticed things falling apart a bit at higher volumes, mostly with the higher freq. output. The subwoofer I have at 50hz and below, and used mostly to add a lithe bit of "pop" to the electronica music I so much enjoy. Room size is smallish, say 12 feet b/w me and speakers, but will probably employing these in a larger space soon.

What should my next step up be? I'm interested in larger, more expansive soundstage. I want more "feeling" the music, with a bit more lower end. I want to try and improve the higher end "shrill" that I can get with higher volumes.

I AM NOT intersted in changing speakers, as I'm very happy with these towers.
I AM NOT interested in chancing cables, as I am just not completely sold on this upgrade path, at least, at the current level of equipment I have.

Would you recommend an outboard amp? Higher power Rotel or musical fidelity, for example? And how much power? ( I do want something that will last a long time, with further upgrades in speakers, and larger power req. in the future)
Would you recommend a change completely from the integrated to a much nicer integrated unit with higher output?
If I were to spend 1,000$ on a newer higher powered integrated vs 1000$ on a power amp, where would I see the MOST benefit.
Would you recommend a change the subwoofer either in addition to, or alone as a substantial upgrade?

I appreciate all your input! My budget is probably in the 1K range.

thanks all!
H