Panel on mobile devices is getting better, especially on tablets. I like the wrapped thumbnail text and the number of albums/tracks in the album cover. But on tablets and especially on phones there are still some issues due to the small size. Here are some suggestions to think about, some based on things I like about Gizmo. All of them are aimed at maximizing usability on a small screen. I understand this is tough when you are designing for both 21" screens and small phones.
1) Thumbnail Size - The thumbnails in Panel should be smaller for a mobile device. If I compare Gizmo, there are 5 albums across and 6 vertically on my small tablet in vertical mode versus 4 vertical and 4 horizontally in Panel - so twice at many album covers with Gizmo. There should be a slider that lets you change the size. Or possible, pinch the touch screen to change the size. Or a small, medium, large checkbox for cover art size.
2) Persistence of Playing Now in Album Cover view - After playing a track, if you return to the album cover views, a small version of playing now stays at the bottom on the screen. On a phone, that takes a significant amount of space. It would be nice to have an option to return to the album view without the playing now information at the bottom. A cover art icon in the top line that skips back without displaying the playing now option could do that.
3) Tag and Track Information To Show on Small Screen in Playing Now - In Gizmo in Playing Now if you hit the list button, it switches between a album cover view with track name, album name and artist name and a track view list. Panel tries to do that all on one screen which means the tag information is either not there or truncated and the list is short. The ability to switch between the two types of views might be useful. One thought is to be able to tap on the cover art in playing now and have it get smaller and show the tag information. This would be a toggle. Particularly helpful on a vertical phone view.
4) Scrolling Track List - In Playing Now, when you scroll both the cover art and the track list scrolls. It would be nice to leave the album art in place and scroll just the track information. In addition, when advancing from track to track, the display does not automatically scroll so when you get to the end of a screen you have to manual scroll to see the rest of the list.
5) Playing Now Tags for Classical - Playing Now shows artist, album and track. This is not optimal for classical music. There should be some way to show composer for classical. It could be inherited from the categories in the view, for example. Using existing tags may not be good enough, since genre could be something like Opera. The simplest way would be to have each view specify the fields to be display, although that mechanism does not currently exist in defining views, other than the categories defined.
For some of these options, they may be only applicable on a small device. A Mobile checkbox in Settings would allow the user to select when to use the mobile settings.
Anyway, those are some of the things I see as possible improvements for mobile devices. You have probably thought of some or all of those things, but hope this helps. Keep up the good work.