[Huawei P8 ROMs, Kernels, Recoveries, & Other Devel] nexolight:
Ok I updated all the partitions. That's how I did it just in case one wan't to do it as well. I will drop the support for the older kernel but I keep the link for it and the recovery there just in case.

1. Download the app extractor here http://xdaforums.com/showthread.php?t=2433454

2. Download the old Huawei UPDATE.APP for 5.0. When the link doesn't work any 5.0 UPDATE.APP should be fine.

3. Download the new Huawei UPDATE.APP. Basically any 6.0 should be fine.

4. Extract both with the UPDATE.APP extractor by using this profile (there's an editable xml):

<Profile name="Huawei Ascend P8 (GRA-L09)" author="Nexolight">
<Files>
<File type="md5rsa" filetype="signature">00.MD5RSA.img</File>
<File type="crc" filetype="checksum">01.crc.img</File>
<File type="3rdmodem" partition="/dev/block/mmcblk0p33">3rdmodem.img</File>
<File type="3rdmodemnvm" partition="/dev/block/mmcblk0p14">3rdmodemnvm.img</File>
<File type="3rdmodemnvmback" partition="/dev/block/mmcblk0p15">3rdmodemnvmback.img</File>
<File type="boot" partition="/dev/block/mmcblk0p27">boot.img</File>
<File type="cache" partition="/dev/block/mmcblk0p34">cache.img</File>
<File type="cust" partition="/dev/block/mmcblk0p39">cust.img</File>
<File type="dfx" partition="/dev/block/mmcblk0p32">dfx.img</File>
<File type="dtimage" partition="/dev/block/mmcblk0p29">dtimage.img</File>
<File type="fastboot" partition="/dev/block/mmcblk0p5">fastboot.img</File>
<File type="hifi" partition="/dev/block/mmcblk0p26">hifi.img</File>
<File type="hisitest0" partition="/dev/block/mmcblk0p35">hisitest0.img</File>
<File type="hisitest1" partition="/dev/block/mmcblk0p36">hisitest1.img</File>
<File type="hisitest2" partition="/dev/block/mmcblk0p37">hisitest2.img</File>
<File type="mcuimage" partition="/dev/block/mmcblk0p3">mcuimage.img</File>
<File type="misc" partition="/dev/block/mmcblk0p19">misc.img</File>
<File type="modem" partition="/dev/block/mmcblk0p30">modem.img</File>
<File type="modem_dsp" partition="/dev/block/mmcblk0p31">modem_dsp.img</File>
<File type="modem_om" partition="/dev/block/mmcblk0p17">modem_om.img</File>
<File type="modemnvm_backup" partition="/dev/block/mmcblk0p10">modemnvm_backup.img</File>
<File type="modemnvm_factory" partition="/dev/block/mmcblk0p6">modemnvm_factory.img</File>
<File type="modemnvm_img" partition="/dev/block/mmcblk0p11">modemnvm_img.img</File>
<File type="modemnvm_system" partition="/dev/block/mmcblk0p12">modemnvm_system.img</File>
<File type="modemnvm_update" partition="/dev/block/mmcblk0p20">modemnvm_update.img</File>
<File type="nvme" partition="/dev/block/mmcblk0p7">nvme.img</File>
<File type="oeminfo" partition="/dev/block/mmcblk0p8">oeminfo.img</File>
<File type="recovery" partition="/dev/block/mmcblk0p28">recovery.img</File>
<File type="recovery2" partition="/dev/block/mmcblk0p21">recovery2.img</File>
<File type="reserved0" partition="/dev/block/mmcblk0p4">reserved0.img</File>
<File type="reserved1" partition="/dev/block/mmcblk0p16">reserved1.img</File>
<File type="reserved2" partition="/dev/block/mmcblk0p22">reserved2.img</File>
<File type="securetystorage" partition="/dev/block/mmcblk0p13">securetystorage.img</File>
<File type="sensorhub" partition="/dev/block/mmcblk0p25">sensorhub.img</File>
<File type="splash" partition="/dev/block/mmcblk0p9">splash.img</File>
<File type="splash2" partition="/dev/block/mmcblk0p18">splash2.img</File>
<File type="system" partition="/dev/block/mmcblk0p38">system.img</File>
<File type="teeos" partition="/dev/block/mmcblk0p23">teeos.img</File>
<File type="trustfirmware" partition="/dev/block/mmcblk0p24">trustfirmware.img</File>
<File type="userdata" partition="/dev/block/mmcblk0p40">userdata.img</File>
<File type="vrl" partition="/dev/block/mmcblk0p1">vrl.img</File>
<File type="vrl_backup" partition="/dev/block/mmcblk0p2">vrl_backup.img</File>
</Files>
</Profile>

6. take an external sdcard and place the new UPDATE.APP into SDCARD: dload/UPADTE.app

7. Now you need to go to fastboot and flash the recovery.img, recovery2.img and boot.img from the old UPATE.APP. Now you should be able to boot into the EMUI recovery as usual. The recovery will automatically flash the dload/UPDATE.APP

This UPDATE.APP contains all the new partitions and I did it this way just to not have to care about doing something wrong. It flashed the stock 6.0 rom including all the partitions quite fine.

The reason for first flashing the old recoveries and boot image is that I started from the 5.0 rom. The kernel which is located in boot.img and recovery.img is not version compatible with the other partitions (so I cannot simply take them from the new stock rom unless these other partitions are updated.). However the stock recovery is needed to flash the UPDATE.APP.

8. Now you're on stock 6.0 and only need to flash my images from the initial post, wipe cache + data and reboot. voilà.