K8098 to be connected to a DOUK preamp ?rca or headphone jack?

Hi all
My first post, be kind!
I have ordered a K8098 preassembled and planning to connect it to a DOUK valve preamp (pics show the unit, it has a frontal headphone out, which i can split with a headphone splitter but prefer not- this would be option 1)
Second option is using the rca output (at the back of the unit).
I have several questions if anyone would be so kind to answer?

1- can i use the headphone output at the from and listen to music, and at the same time wire the k8098 at the back on the rca R+L outputs? I am not really sure the preamp disconnects the rca output when i am using the headphones?- the manual only says the rca level is “2.3v” (see pictures).
Output of headphones jack is 100mw @ 32 ohm.
if it is of any help, i tried to figure out if i can use at the same time the headphones at the front , and the rca output at the back, but i only had another pair of headphones to do the try, and when connected to the rca output at the back of the unit ( i think it might be because the impedence if the headphone 32 ohm is too much?)
2- i already have a second vu meter (also picture of it attached) which i was wondering if i can use at the same time (ie current vu meter split with headphones and k8098 connected at the back via rca output).
3- if i use the rca at the back, do i need to put a “10k resistence” on each rca positive wire to have stereo reading? K8098 manual not too clear about this. Also, the negatives (grounds) of the R and L rca, do i connect them together or do i use just one of them (ie i dont need 2 negatives going to the k8098).
By the way those connected at the front do still work when i do this.
Sorry if i said something that doesn’t make sense, i have done soldering and little projects for years but not really a preamp/hifi expert
Cheers all