Audio stretch a whole song with wav-files? Best practice in X1?

Hello Please bear with me, this may take a while... I am going for my first attempt to remix a track. I have some wav-files, and want to add some basslines and drums. However the wav-files are 128 beats long and contains the whole song (including silenced parts). Thus, I am not sure of the best way to change the tempo of whole audiotracks (not shorter samples) into something I can work with. Normally I might do this by making the audiotrax as loops clips or working on them in the Audiosnap tool and bounce to clip. However, this process don't seem too clever for whole tracks? It's far more easy with samples or shorter pieces of audio. Is this the way to proceed? I would be very happy for some help in the right direction:) Some fact. Tempo of the audioclips: 148.724 bpm (according to loop constructor) Beats in track: 128 Seem like a strange tempo in the first place!? This is what I want to do: 1. Get the correct tempo of the wav-files (128 beats long). 2. Tempo sync the whole audiotrack so I can fit it into the tempo of the song. (i.e. kickdrum on 1, 2, 3, 4 in 128 bpm). 3. When in sync I might edit them further and want the audioclips to easily be moved around in the song. 4. Insert a new bassline and/or drums with the step sequencer or midi (and start on the correct timing). Thankful for any input on this subject:)