I think we all bring something to this forum in the way of specialised knowledge. In my case it is sound. I have been an ardent Hi Fi enthusiast for well over 40 years and to that end feel a tad qualified to write on sound reproduction.I've got my Z on ebay, sitting in front of me waiting to sell right now. I wanted so much to love the Z and still do love the Water resistance and ruggedness, as well as the size of the screen. Simply put though, the Z falls down on too many points.
Z points;
Camera : Very good, although no better than S3 or iphone 4 or 5 for that matter.
Music: Too quiet, although sound quality is great. The low volume overall, especially through the headphone socket, even with audio mods, is inexcusable from Sony.
Screen: Sony have basically just slapped a small computer monitor screen on it, as the viewing angles remind me of PC lcd screens.
Viewing angle is the big no no here, it is almost useless viewing texts with phone on desk, and watching a movie or looking at content with a friend on the screen is very disapointing.
Performance: The Z is slightly too laggy, although it is very fast.
I love the size of the Z screen and the software is very nice, especially the album app, which is hands down the best album app i've ever used.
Sony fell just short of the mark with this. Given the choice again, I would not of bought it. The HTC One i've replaced it with beats it in every respect barring screen size and water resistance.
In terms of your comment regarding the volume levels when using the head phone socket I ponder if, in truth, you have in fact actually either owned the XZ or used one? I confront you openly with this as to write that the sound level when using head phones is too low is simply untrue unless you have some hearing problem?
Upon reading your post I performed my own mini test using the following head phones and in ear head buds;
Sennheiser MX90 VC. Sennheiser CX300-11. Sennheiser PX 100-11. Pioneer SE-MJ751
The above range from in ear buds through on the ear mobile head phones to in house full head phones.
I also used the SXZ, LG P880, Samsung Galaxy S3 and the SGNote. (Not today but last week I also used the HTC One though not as a test in itself.)
In relation to sound reproduction. All four produce a decent acceptable sound meaning listening experience was acceptable considering what the device is IE it is not the 10 grand set up I have in my living room.
Sound reproduction is a very subjective experience, what some will enjoy others will not. In terms of the overall experience all four reproduce music well. Please remember that often the closer we hear the true recording it can be the case we dislike said rendition. With zero adjustments to any music parameters and using the same music player installed on all four devices I can report the most faithful to the original recording is the Sony.
Secondly the volume on all four was way above the dB level for safe hearing on all phones used.
To this end it is difficult to accept your comment on the volume levels of the XZ when used through the head phone port. It simply fails the litmus test and is technically inaccurate.
Now speaker...The Sony is simply diabolical. The Sony reproduced distorted sound at any volume past 50% operating level. The Note offering the best experience even though that is also awful. I must add that these are mobile phones and not music centres.
I have a family member with the HTC One and the sound reproduced from the speakers is in a different league to the other mobiles mentioned. I must again add that even the HTC is not something I would consider even close to a decent listening experience using the two front facing speakers though. I will also add that when using the HTC One through the head phone outlet the reproduction is 'different' to the above mentioned mobiles but that is all it is, different. This is where personal taste come in. In terms of faithful reproduction of sound recording again the Sony wins the day.
With regard your attention to viewing angles. I have no idea why any owner would desire to hold the mobile at a 45 degree angle to their line of vision? This again harps back to perhaps you having read reviews where this criteria is used and mentioned as a negative? This IS a mobile phone and not a TV. Personally I like the viewing angles as I don't rely care for the person sitting next to me three seats away reading my mails.
I hope you enjoy the HTC experience. I have owned numerous handsets from that brand. Back to the HTC One. The main reason I HAD to stop purchasing HTC mobiles was the signal strength. I live way out in the countryside and signal strength here is abysmal.
Nokia have produced the strongest signals but I can't get along with their OS. HTC have been the weakest and Samsung have proved not to bad. The Sony, thank heavens, is by far the best of the non Nokia handsets. The HTC One doesn't pick up any signal here at all. That fact alone makes the HTC a non starter for me also the lack of expandable memory. Different mobiles for different tastes.
Regards.