Tubes for a pre stage... matched NEW or unmatched identical NOS?

The Sphinx likely uses tubes for the phono section, so low noise is paramount.

For maximum RIAA fidelity and channel balance, the g1/g1 and g2/g2 sections need to be well matched, assuming the same topology for each channel.

The big fly in the matching ointment is that tubes seldom match across the entire operating range and matched tubes are matched in a matcher, NOT your amplifier and thus operate under totally different conditions. Tubes matched on one matcher may have very different numbers on another matcher.

Tubes matched today aren't matched tomorrow as they age at different rates.

See ieLogical Rolling

from stereophile’s review of the sphinx v3

Description: Hybrid integrated amplifier with 12AU7 tubes in line stage and class-D output stage. Power output: 100Wpc into 8 ohms (20dBW), 200Wpc into 4 ohms (20dBW). THD: <0.1% typical, <1% at rated power. Frequency response: 5Hz–20kHz, ±1dB. Input sensitivity: 1.0V RMS. Power requirements: 115/230V–50/60Hz.

12au7 pair is in line stage, not phono stage (which is solid state)...

...not to say that matching and low noise are not important, but just significantly less so than if it were in the phono stage

12AU7-based mu-follower preamplifier stage driving a 100Wpc (into 8 ohm), class-D, solid-state power amplifier

A mu-follower has plenty of gain which has to be padded down to drive the Hypex UcD-180 Class D. Weird.

Everyone should figure where the bottom line is located and how it works.

It's extremely simple and safe to assume that dealers pragmatically label the tubes they sell to you as matched while in reality it's just a tube and sometimes even cigar is just a cigar.

FYI, I really haven't enjoyed any newer tubes, all of my favorites are NOS. I do use matched tubes for each channel of my 2 channel amp.

For the money, it is very hard to beat 1960s RCA "Clear Top" tubes; you can usually find them for about $20 or so each and they are terrific.

If you want next level it will cost you, I really enjoy Amperex tubes. My favorites are Amperex 7308 PQs, Amperex 7316 "Long Plates", Amperex 6922 PQs, and Phillips 12AU7s.