THe SP9 is a very nice preamp
I own the LS 5 which is all balanced ins but is a spectacular preamp - more open than the ref-1
a very musical piece - light years above the LS2 I had before
an LS 15 16 or 22 is a lateral move, you are not really gaining anything
You might consider a Steve Huntley upgrade to your sp9
Steve worked for Audio Research, Wadia and Cal Labs as a designer, and makes significant upgrades to the pieces using the latest electronics and knows where each units limitations were. He has several levels of upgrades for specific Arc pieces and is very knowledgeable and straight forward. I'll be sending him my preamp.
do a search on gns here at audiogon, my friend has an LS22 and it really opened it up