I own the SLP-98 and have heard both the 98 and the QS Linestage on five different systems at least. Each Pre-Linestage has it's own presentation and they do sound different in stock form, and both benefit greatly from really good cap and tube upgrades. My SLP-98 feeds QS Mono 120 amps with KT150 tubes, and its a nice synergy.
While I prefer the SLP-98 and 6SN7 tubes more (after the upgrades are made and with the right 6SN7 tubes in play), the QS is really nice too (and a great value), and even better once the upgrades are made and with the right 6DJ8/6922 tubes. The SLP-98 comes stock with two sets of Pre-Outs, and this is nice if you have a dual subwoofer setup. Mike at QS can modify the QS Linestage and re-use the Tape Out to reconfigure it as a 2nd Pre-Out set if you need to for subwoofers, and he's charged a few friends about $45 for the TapeOut-PreOut mod. Can't go wrong with either.
While I prefer the SLP-98 and 6SN7 tubes more (after the upgrades are made and with the right 6SN7 tubes in play), the QS is really nice too (and a great value), and even better once the upgrades are made and with the right 6DJ8/6922 tubes. The SLP-98 comes stock with two sets of Pre-Outs, and this is nice if you have a dual subwoofer setup. Mike at QS can modify the QS Linestage and re-use the Tape Out to reconfigure it as a 2nd Pre-Out set if you need to for subwoofers, and he's charged a few friends about $45 for the TapeOut-PreOut mod. Can't go wrong with either.