I am not an expert on dap soundstage but I do know live music very well. If a large soundstage means a decrease in detail and clarity of instrument's and a main focus on vocals then it is not what I would want in a dap soundstage. From what I've read on soundstage : "
The term soundstage refers to the depth and richness of an audio recording and usually relates to the playback process. According to audiophiles, the quality of the playback is very much dependent upon how one is able to pick out different instruments, voices, vocal parts, and such exactly where they are located on an imaginary 2-dimensional or 3-dimensional field. The quality of this soundstage can enhance not only the listener's involvement in the recording, but also their overall perception of the stage".
This explanation of soundstage is not what I am experiencing with the x5ii.
Actually, I really think, as
@KLJTech said that you would enjoy something else better.
X5II has a large soundstage, up to high end devices soundstage, and using something like m50 or im02, you are getting to get a dispersed sound, and lack of details because of the headphones not actually being able to keep up with what is there. Simply put, the headphone renders the outer sounds as much quieter, because those two models are not the best at rendering outer sounds, while the front sounds are rendered louder, and much clearer. So you will get something you might not like, some people actually like this sound. Most smartphones are very 2 point soundstage-like having something like a stereo, and you actually get to hear most details with m50 or im02, but those two headphones were projected to be used with this type of sources, so they actually do a great job, making these sources sound very clear and exctracting details out of them.
I have an HTC 820, and tried it with lesser headphones/IEMs, and it really shines there. When I plug in IE800, which picks EVERYTHING the DAC and AMP put out, all my other devices sound very bad, simplly because IE800 reveals their flaws.
If you really like your phone better, you should stick with it, as the most important part is how to have the most fun with this hobby.
About the lasts posts, every smartphone I had tried as an audio source is a long distance behind in terms of everything audio compared to X5II, but it really is a matter of taste, I remember that when I first got X5 and used it with my IE800, (coming from a cowon j3 + ie8) the sound took a while before I could truly enjoy it, as the details and everything was quite different, and the things I used to love about certain songs disappeared (j3+ie8 used to blur everyting, but still have a large soundstage, like creating a sound of no distinct guitar, or no cymbals, but there still was a guitar sound coming from literally everywhere. It sounded very wrong considering the real deal, but it had it's fun) and there were new things emerging from every song. It is evident, when something like Breaking Benjamin used to have a smooth melody line with a cowon j3 and ie8, and now you can hear a distinct single guitar, with a background guitar, a voice and lots of cymbals. Nowdays I like it much better this way, it is much better, and I would never go back.