The way I see it is this!
If you had ISO17025 before you were/are going to be QS accredited then you must have done this for a reason. Ask yourself - what was that reason?
Even if you are ISO17025 accredited, this does not mean you will meet the requirements of lab control for QS9000 (but you probably will). You still need to meet ALL the requirements of QS9000 separately.
If one of your customers requires you to have ISO17025, they won't be impressed if you've decided to leave out ISO17025 and go for QS9000 instead.
I really think you need to keep both because QS9000 is an automotive quality management standard that gives “minimum requirements” for in-house Lab control, and I would imagine it doesn’t come close to meeting the requirements of a Lab accreditation cert. Not by a long way!!!!