Those mentioned are not av pre-amps, they're av amps and not using the poweramp stages, or 3 channel av pre-amp/processor. Av pre-amps cost a lot of money.
Second hand there are the Tag and Lexicon DC/MC processors. The Lexicon don't have analogue 5.1 inputs however they're renowned as superior units in processing (Logic 7)
New there's Naim- about £3000. Arcam I think that's £2/3K. Lexicon MC-8/12, somewhere between £5-£12K. Yamaha are miles behind in processing and power amplification. Crap.
I've got a Lexicon MC-1, it's fab. The lack of 5.1 inputs (or HDMI) wasen't a concern, but if you're going into new formats then have to make a choice. Processing on top-end processors is superior to new budget av amps. DC/MC are about £400/£500. The MC-1 is superior processor than the DC-2 (higher quality DAC's)
If you do buy a Lexicon- DC-2, make sure it has the DTS board fitted, and with Dolby Digital option,with latest firmware -V4. When you switch it on it'll display
V4
AC-3 DTS.
The MC-1 comes supplied as standard with DTS & DD, but again check for latest firmware. On both Lexicon's, V4 also adds THX Surround EX. It also has other THX options, two useful modes are re-equalistation and subwoofer peak protection. The Lex's can upscale stereo to full stereo sides and surround 7.1, and it sounds great. For music, I recommend Music Surround. You can have settings per mode, Logic 7 music & film settings By default re-equalisation is enabled for all film Logic 7 modes, so disable them. Only need it if your centre is a bit harsh on the top end (probably cheaper centres) It's disabled by default for all Logic 7 Music modes. You can have seperate settings for 2 channel ie.
Calibrate.
2 channel
Subwoofer -6db
Logic 7 Music DTS
Subwoofer -4dB
*
Logic 7 Music Dolby
Subwoofer -3dB
*
Logic 7 DTS
Subwoofer - 00dB
*
Logic 7 Dolby
Subwoofer -2dB
*- denotes you can tweak other speakers channel levels.