Seeking more 3d imaging, deeper/wider soundstage

I think my DAC actually inverts phase, I think I read that somewhere. So to invert phase - I swap the output cables coming out of the DAC, right? Or do I swap the speaker cables at the speaker end? Or does it matter?
My only concern with vintage tube gear is maintenance. Where can I get that stuff serviced?
I am interested enough in tubes to definitely try them. I have a lot of research to do to familiarize myself with the different brands.
@ Raymonda: Wild Beasts, Proem, Coldplay, Bola, Coppice Halifax, Muslimgauze, Fuck Buttons, Miles' Birth of the Cool, Yeasayer, Demdike Stare, Andy Stott, The Berlin Philharmonic's recording of Holst's Planets, Amon Tobin, Haxon Cloak, various Beethoven symphonies conducted by Karajan, James Blake, numerous Hans Zimmer soundtracks, Moderat, Om, Love and Rockets and even Vampire Weekend, I consider all of these to be high-quality level recordings or artists who produce them.

Realremo - Atmasphere's comment related to the speakers themselves being out of phase not the musical signal itself. Make sure the + and - from the power amp goes to the + and - to the speakers. If one is incorrect, then the images will be outside of the speakers rather then in between them.

Concerning the signal itself being inverted, you could resolve this by inverting the speaker cables at both speakers .but I don't think you will notice much here. I had a DAC with an invert switch and I could flip it again and again and no way would I ever pass a blind test that anything was changing.

Concerning repair of vintage electronics, there are such repair places all over the country. And people here would be able to point you in the right place with a simple query. Some of the companies in my list, CJ, BAT are still in business.

Tubegroover - You will notice that I had no ARC products in my list. And this is because, for me anyway, the ARC magic starts with the SP-8, and this typically sells in the $1500-1900 range which is outside of the budget here.

A suggestion that won't cost a dime: Move your speakers further apart and/or bring them out into the room some more. Also, experiment with more drastic toe in once you've spread them apart. You may be surprised.....

Realremo, to check to see if your speakers are in phase, you simply reverse the connections on the back of **one speaker only** - not both.

If this works, you will immediately notice greater center fill and sharp images between the speakers. If it does not work, the images will become more diffuse.

Regarding tube equipment reliability: tube amps and preamps are usually fairly reliable- some more so than transistor equipment- it depends a lot on the manufacturer. The issue is the tubes themselves, which are considered user-replaceable, which is why they are in sockets. When a tube goes bad, quite often it will tell you about itself :) So you don't have to send the product somewhere to get serviced, you simply replace the tube and you are down the road. If it were any other way it would not be possible for tube equipment manufacturers to be in business for decades at a time!

Its important to distinguish between the reliability of the chassis as opposed to that of the tubes. For example in our amplifiers if a tube fails it will not damage the amplifier (although it could blow a fuse); our amps are stable enough that I have a demonstration I do at audio shows where I remove power tubes from the amp while it is playing music. You don't hear any change- the amp continues to play as if nothing happened. Now not all tube amps are like that but OTOH its not really important- they will hold up just fine, hence the existence of used tube amps that are heavily sought after 50 years after they were made!!

IOW don't worry about the reliability. Right now it seems you have bigger fish to fry. Keep us informed of your progress.

Realremo, no worrries, mate, there's a very good chance the next CD you play is also inverted phase, so it all evens out. Always look on the bright side.