Well, opinions from folks actually owning these devices is needed; neither doubting quality nor speculation will help the OP or anyone else interested in these hybrids.
In the late '90s, early 2000s, Musical Fidelity offered the X-Cans, then X-Can II and X-Pre line of hybrid headphone amps and preamps respectively. Also, let's not forget their famous hybrid buffer unit, the X-10D, plus a neat X-Tone bass and treble tone control module. These came in very cool looking, almost identical cylindrical cases. Folks, they didn't just look cool; they sounded very nice. These each ran off 12VAC wall warts, which could easily be upgraded with beefier 12V AC output wall warts. Internally, each X- device cleverly splits the 12VAC into DC filament supplies as well as plus and minus 24-30VDC B+ rails. So, that is nearly 60VDC, low for some tubes, but fine for the 6DJ8/6922 family. MF even offered a similar looking X-PSU, quite collectable today, which could power 3 or 4 X- type devices. Presently, some of these X-types have morphed into MF units with different looking cabs and supposedly updated circuitry. The originals were quite a breakthrough and paved the way for copycat, less expensive, less ornate looking, hybrid headphone amps/preamps with clear plastic tops and cool looking LED underlighting. Then, later came the swarm of metal looking copycat devices and some were even metallic chassis equipped. Some sound surprisingly good...
History aside, probably the most "popular" of these copycats was the Indeed tube hybrid headphone amp. When they arrived on the scene, they cost about $100. delivered from HK or China. Reading some of the early online reviews, I surmised this device could become a preamp of sorts. With an ability to drive 32 to 600 Ohm cans (headphones) very loudly with low distortion, they could more easily drive higher impedance devices, like tube power amps. The first version Indeed hybrid 'phone amp only had a volume control and headphone output jack on front, plus input RCA jacks on one side, IIRC. I quickly bought one for about $80. delivered and was quite amazed how good it sounded with 32 to 600 Ohm cans. I wired a stereo cord, 1/4 inch stereo headphone plug to stereo RCA plugs. Since these devices could easily drive low impedances, 2 to 3 meter long "interconnects" were fashioned and tried with numerous systems I had around. These were pleasantly surprising and successful, sonically virtuous devices !
Flash forward about a decade, long after two birthday presents of the next generation, Indeed Gen. 2; one for my son-in-law and one for my daughter. As they listened for the first time, smiles were inherent. Still today, they still use 'em and smile while listening. Personally, using them as an interface between musical sources and power amps, I was amazed at their large degree of gain with low coloration. Used as a buffer with gain, they improved the sound of digital sources immensely and perform preamp duty well.
The Indeed Gen. 2 and now Gen. 3 offered more useful options and advertised themselves as hybrid headphone amps/hybrid buffers and preamplifiers. Their volume controls track well. They can switch inputs between RCA input jacks or 3.5mm mini-stereophone input jacks, 6.3V or 12V tubes (!), plus have RCA output jacks. Besides their versatility in impedance matching and tremendous gain with low distortion, their sound quality is surprisingly very fine. Of course, replacing the included tubes can be beneficial and avoiding the sometimes offered strange tube types can be in order...
I can vouch for the Indeed first generation 6922 hybrid headphone amp, Indeed Gen. 2 and the half priced Lil Bear P1 which apparently copies the Indeed Gen.2. The second generation units can switch between 6922/6DJ8/ECC88 or ECC82/12AU7 tubes ! There are numerous online sites for research; some even examine upgrading and optimizing tube bias when swapping tube types. The infamous rockgrotto forums have catered to upgrading the X-Can and X-Pre devices. I also own a genuine, MF cylindrical X-Pre line stage preamp which will only be upgraded when needed and probably kept for another two decades...Research is recommended, then choose after reviewing actual owner opinions...
