What to upgrade?

Looks like a good amp and nice speakers. You probably just need to add a little "muscle" in that larger sized loft to retain good dynamics at higher volume.

If sound is good but dynamics lacking at higher volume, I would consider adding a pair of good powered subs. That's the easiest way to just throw some more power and air pressure at the problem. Crossing over to subs for low bass will also take load of the monitors and allow them to do better as well at higher volumes.

Do you use any room treatments for the acoustics?
That could possibly be the culprit?
With that said I must admit that I'm not familiar with your current speakers or integrated amp. Can you tell me more about them?

No doubt room acoustics in a loft can be tricky. Might wreck havoc on soundstage and clarity with perceived dynamics more the victim.

DEfinitely always a good idea to assess and get a handle on teh room acoustics before making a major change. That's often the biggest determining factor regarding what will or will not work. Good sound from gear heard elsewhere may not matter much.

The sub idea might still be the effective boost needed. Placement options with separate subs to compensate for room acoustics might be easier than just replacing with all self contained larger speakers. Corssed over correctly, existing amp should be able to perform more optimally as well at higher volumes with low bass offloaded.

Take a look at some of the audiokinesis Planetarium speaker systems that leverage up to 4 separate subs to help compensate for room acoustics. This might be a fantastic approach to consider in your case. I have not heard these but love the innovative approach and thought processes that go into Duke's stuff to wean out performance for reasonable cost.

Thank you for the response.

Mapman - The dynamics seem to be ok at higher volume but the highs and midrange get a bit lost with no separation of instruments. I have given subs a thought. Just not sure how placement would work and not sure how one goes about connecting them. Any ideas of a sub that would match my system?

Lak - I have also thought about room acoustics and have researched but just have no idea of what I would need. Noted below is some additional information about the speakers and amp and room:

Daber Audio Monitor 3 daberaudio.com
Features/Specs
8 inch Magnesium/Aluminum woofer
2 inch Aluminum dome midrange
Planar Tweeter
Satin Nickel binding posts
Hand built crossovers using hand selected parts
150 watt RMS power handing
91 db efficiency
35-21k response
8 ohm nominal impedance
Rear facing port
32 pounds each
22" H X 9" W X 14" D

Portal Panache portalaudio.com
The Panache Integrated Amp by Portal Audio combines a completely transparent passive line stage with a high gain dual mono Class A/AB amplifier on one chassis.
100 w X 2 @ 8 ohms
200 w X 2 @ 4 ohms

Room
One speaker is in a corner, Back wall, side wall, cabinet, the other is open on the left side, back wall, cabinet on the right side.