could not mount specified root try again (fake raid)

пробовал уже с ключами --dmraid и от безысходности --mdadm)

Вы в курсе, что документацию нужно всё же читать, а не открывать и закрывать?

параметры ядра указываются в отдельной строке, начинающейся с "options=" в файле /boot/efi/EFI/refind/refind.conf в соответствующей секции, так же ещё есть файл refind_linux.conf, пример которого вы сможете найти в /usr/share, просто посмотрите список файлов в пакете с refind.

rEFInd supports semi-automatic Linux EFI stub loader detection. This feature works as part of the standard boot loader scan operation, but it extends it as follows:

    rEFInd looks for boot loaders whose names include the strings bzImage or vmlinuz and that end in .efi. For instance, bzImage-3.3.0.efi or vmlinuz-3.3.0-fc17.efi would match, and trigger subsequent steps in this procedure. Beginning with version 0.3.0, if you uncomment the scan_all_linux_kernels option in refind.conf, rEFInd will also scan for kernels without a .efi filename extension. This option is uncommented by default, but if you comment it out, delete it, or change it to read scan_all_linux_kernels 0, rEFInd won't scan for kernels that lack .efi filename extensions.
    If a file's name ends in .efi.signed, any other file with an otherwise-identical name that lacks this extension is excluded. This peculiar rule exists because Ubuntu has begun delivering two copies of every kernel, one with and one without this extension. The one with the extension is signed with a Secure Boot key; the one without it is not so signed. Thus, if both files are present, the one without the key won't boot on a computer with Secure Boot active, and either will boot if Secure Boot is inactive. Thus, rEFInd excludes the redundant (unsigned) file in order to help keep the list of boot options manageable.

    A kernel whose filename lacks a version string matches an initial RAM disk that also lacks a version string in its filename. Note that you can reliably use only one kernel and initial RAM disk per directory that lack version numbers in their filenames.
    rEFInd looks for an initial RAM disk in the same directory as the kernel file. A matching initial RAM disk has a name that begins with init and that includes the same version string as the kernel. The version string is defined as the part of the filename from the first digit to the last digit, inclusive. Note that the version string can include non-digits. For instance, the version string for bzImage-3.3.0.efi is 3.3.0, which matches initramfs-3.3.0.bz; and vmlinuz-3.3.0-fc17.efi's version string is 3.3.0-fc17, which matches initrd-3.3.0-fc17.img. Many other matches are possible. If an initial RAM disk is identified, rEFInd passes a suitable initrd= option to the kernel when it boots.
    rEFInd looks for a file called refind_linux.conf in the same directory as the kernel file. It consists of a series of lines, each of which consists of a label followed by a series of kernel options. The first line sets default options, and subsequent lines set options that are accessible from the main menu tag's submenu screen. If you installed rEFInd 0.5.1 or later with the install.sh script, that script created a sample refind_linux.conf file, customized for your computer, in /boot. This file will work without changes on many installations, but you may need to tweak it for some.
    If rEFInd can't find a refind_linux.conf file in the directory that holds the kernel, the program looks for a file called /etc/fstab on the partition that holds the kernel. If this standard Linux file is present, rEFInd uses it to identify the root (/) filesystem and creates two sets of Linux kernel boot options: One set launches the kernel normally, but with minimal options, and the other set launches the kernel into single-user mode. This step can get a computer to boot without any rEFInd-specific configuration files, aside from refind.conf in rEFInd's own directory, but only if /boot is not a separate partition. The intent is to facilitate the use of rEFInd as an emergency boot manager or to help users who must install rEFInd from OS X or Windows. Note that rEFInd uses /etc/fstab only if refind_linux.conf is not found.

Удачи, читайте документацию и следуйте ей, у вас всё получится.

UPD:
Если у вас многоядерный процессор, то отредактируйте конфигурационный файл genkernel и задействуйте многопоточную сборку ядра и модулей, а то по умолчанию образ ядра и модули собираются в один поток, либо собирайте ядро вручную, а не посредством Genkernel, т.е.:

cd /usr/src/linux
make menuconfig
make -j4 bzImage
make -j4 modules
mount /boot
make install
make modules_install

а посредством genkernel собирайте только initramfs:

genkernel ramdisk ....

При многопоточной сборке ядро на оптимизированном конфиге ядра и модули к нему, при сборке в 4 потока, может быть собрано за 5 минут и даже быстрее, а не пол часа, в лушем случае, при сборке в один поток.