From Stereophile-
"...Like the PS Audio 4.5 and 5.0 when used in their purely passive modes...demonstrates all too clearly that many preamplifier designers have spent too much time on their phono stages and too little in making sure that their line stages are totally neutral. The vast majority of high-end preamps simply cannot meet the challenge of the equivalent of a straight wire bypass with controls. As a result, it is clear that you can get a unit for $400 that will outperform most active preamps, including some costing six times as much...This raises the alternative of the PS Audio preamps, which also provide an affordable way of getting what is basically a passive high-level control center. The PS Audio 4.5, for example...includes an excellent moving-coil/moving-magnet phono stage and a good switchable line stage....—Anthony H. Cordesman"
"The next logical step up for me and my budget was PS Audio. I owned a succession of their preamplifiers—4.5, 5.0, 5.5—all of which had many fine qualities like low-noise moving-coil sections, outstanding soundstaging, impressive image specificity, but some serious shortcomings, such as threadbare midrange, chilliness on top, and a fondness for amplifying RF. Neutral-sounding, you say?
No way. Colorations? Clearly. Colorations I had to work around in reviewing other components. Still, the PS Audios were nice pieces for the money. -- Michael Fremer"
From PS Audio's web site discussions-
"...speaking of switches, i have recently gotten a ps 4.6, which i have grown very fond of. however the switches are hard to turn and also have some play in them....Those switches were not great and in hindsight, the real weakness of that design. Be thankful they still work..."
Here's a PDF reviewing a 6.0, but mentioning a 5.5 (similar to the 4.5) often in a direct comparison...
http://www.theaudiocritic.com/back_issues/The_Audio_Critic_18_r.pdf