My only idea is this: At one time I had a NAD 304 as my preamp, and I went with a Quicksilver Linestage using 12AU7 tubes (it was a very early model, SN 0005). That single change was as big a step up as I've taken since I've been doing this hobby.
Not a recommendation for a Quicksilver, but a recommendation to follow through on your hunch.
Not a recommendation for a Quicksilver, but a recommendation to follow through on your hunch.