Here's a few themes from the VF5 series, all looping. No character themes here, just some menus and credit themes that I like.

VF5 Main Menu -> Ruin 65 1st / TEKKEN 7 VF5 Selector -> Hwoarang Stage (Arcade ver.) / TEKKEN TAG VF5 Customization -> Nothingness / TEKKEN 4 VF5 Quest Mode -> Abandoned Temple Final 2nd / TEKKEN 7 VF5 Ending -> Kyoto, Japan (Arcade ver.) / TEKKEN VF5FS Main Menu -> Turbo Electric / TEKKEN 5 VF5FS Customization -> Elegance in Violence / TEKKEN 5 VF5FS Ending 1 -> Forest Law (Console ver.) / TEKKEN 3 VF5FS Ending 2 (Ai wa tsuienai) -> Anna Williams (Console ver.) / TEKKEN 3 VF5US Main Menu -> Windermere, U.K. (Arcade ver.) / TEKKEN VF5US Selector -> Distorter 2nd / TEKKEN 7

To install, place the paks of your choosing in C:\Program Files (x86)\Steam\steamapps\common\TEKKEN 8\Polaris\Content\Paks\~mods