Best Upgrade?

Here is an interesting question. My system presently includes:
EMM DAC6e/Philips 1000
Hovland HP100
BAT 75se
Alto Utopia Be
Synergistic Resolution Reference cables
PS Audio Ultimate Outlet

I am thinking of the next upgrade but obviously can not hear components at home. Either change the HP100, or add a 75se to turn it mono at 150Ws, or get better power conditioning?

How does one really make a good decision given all the variables?

Consider power conditioning as your next upgrade. I've found the Sound Applications XE-12s a real bargain now that the Linestage model has come out. Also consider an Elrod EPS-2 Sig 20A PC. You won't be disappointed. Dead quiet.
Not sure what is meant, when you say "...but obviously can not hear components at home"?

However, I would suggest that you consider investing in those upgrades that help you establish the strongest foundation as possible for your music system. Others may have various opionions as what should be done first, but at least consider power, room acoustics, and vibration management.

Power conditioner can help, but do you have dedicated lines to your equipment and high quality outlets yet?

Have you done anything to address acoustics, either first reflection dispersion or bass management? Is your speaker-to-listening position ideal? To me, room acoustics was the biggest improvement in my system.

Do you have well designed shelf units to support your equipment, and spikes/cones or other devices to couple or decouple your equipment from vibrations? Do you have your cables off the carpet?

These are just examples of the things that can be done with room acoustics, vibration management and power management. Its my experience that you can't really tell what you have in the way of musical quality or deficiencies until you really hear your system in an environment that addresses the three foundation building components: power / acoustics / vibration.
Thank you all. I think I will focus on room accoustics first. Changes in speaker positioning can be heard loud and clear and my room is a little bright given that it is full of glass windows. Interesting though that there is no consensus!
Very best. room is (...) is full of glass windows.
It sounds like there's not a whole "damnation" of a lot you can do about room treatment (heavy velvet curtains @ 1st reflection points??? Even that might only work over ~5kHz or so).

Rather than strain the purse with expensive h/ware upgrades (at yr level, "better" would mean giga$), why not play with the following cheaper "passe-temps":
-DIY power cables
-A transformer coupled volume control -- disconnect the pre(diyhifisupply in HK has a good one)
-Try power amp plugged directly into wall socket (then, pre+power)

If you DO consider there is significantly more to be had from yr (excellent) system than you're getting, I would try a different pair of (94+db sensitive) spkrs. Obviously not at home, as you note -- but @ a dealer???
I just added a BPT 3.5 Signature to my system. I do have a 20 amp dedicated line with hospital grade plugs. It is without doubt, the most incredible update that I have EVER done. I am just stunned at the difference in the sound. The suggestion above, that you begin by building a solid foundation, is dead on target. I have been upgradeing for about 8 years and not one upgrade made as big an improvement as this power conditioner.
In this order, I agree with Mihalis that the room and equiptment placement would make the most noticeable difference. Secound the power conditioner along with good power cords. They don't have to cost a million bucks, but maybe a couple of hundred. The difference I say was amazing. I would recommended this before upgrading your components.