MUTEC MC-3+ USB by Jules
Short version - it makes a great converter sound even better.
Long version: While researching my most recent audio passion - HiRes audio (listening to recordings delivered in resolutions higher than 44.1k 16 bit "CD quality". I stumbled upon HiRes enthusiasts that were raving about this device so I felt I had to try it out.
I already have a high quality converter for listening to music playback, a Grace Designs M903 d/a converter and headphone amp.
I listen to the Grace via Sennheiser HD580 headphones and a pair of ADAM Artist 5 self powered monitors & ADAM Artist Sub unit.
Previously I just fed the Grace USB from my laptop.
I did my listening tests with various albums I have at 96 / 88.2 / 192k 24bit. I normally play these files back via Audirvana Plus software that connects to my Qobuz Sublime Plus account (allowing me to stream hi res audio via wifi) However switching quickly to change between USB to the Grace and Mutec re-clocked USB to the Grace was difficult with Audirvana so I used the Qobuz Mac app for playback. (Its also very good sounding although I feel Audirvana version 3.0.6 has the edge) This way I am able to switch fairly quickly between the converter receiving USB directly from my Macbook's USB output (via a USB C to USB 3 hub) and receiving re-clocked USB signal from the Mutec. (the Mutec receives the signal via USB 3 and sends it out into the Grace via AES 3 XLR)
So I just toggle the AES / USB input selector on the Grace M903 and also toggle the "output device" selector within Qobuz to hear the difference.
Pop / Rock music listening
I have been enjoying The Essential Michael Jackson at 96k 24 bit. The tracked vocals are the first stand out in HiRes. The re-clocked USB signal via the Mutec sounds instantly "wider". Oddly enough it sounds a little 'softer' but thats a good quality because it sounds more 'lush'.
Listening to The Man in The Mirror I found I was suddenly following the bass line when I hadn't noticed it that much before. The kick drum sounds more 'deluxe' and classy via the Mutec and harder and less full range without.
All the different 'spaces' in the production become clearer, you can hear the different reverbs and depths of the (simulated) acoustic space in the production.
Things generally sound about 20-25% better with the Mutec. Spectacular vocals sounded MORE spectacular.
Classical / Baroque music listening
With the Mutec MC-3+ USB listening with headphones it felt that my hearing extended to the very outside edge of the headphones. When disconnected, the sound collapsed inwards to sound less wide and more next to my ear.
Cello and violin "bow scraping' sound on the stringed Baroque chamber music sounds more present, lifelike and seems to have a more extended frequency responce, the same goes for harpsichord.
Over all I found that the Mutec MC-3+ USB supercharged my playback very nicely.
It also had one very unexpected and welcomed benefit. The Qobuz subscription I have streams HiRes over wifi and as the download progresses the playback can sometimes falter and drop out. This is very annoying but I tolerated it. Because the Mutec MC-3+ USB probably has a buffer in the chain for processing, the streaming dropouts never catch up to the output and get 'ironed out'! They have disappeared totally! For streaming 96k and 192k music that is fantastic, no more glitches!