ARC LS7 vs LS16/I

Die hard audio research fans here will tell you whichever newer model, in stock form, will sound better than the old one. You should even "use the stock Sovtek or EH tubes that Audio Research handpicks for you when you send it in."

LS16 has "JFET input stage followed by a cathode-follower/output driver stage utilizing two 6H30 twin-triodes" In English: NOT PURE TUBE.

I have not heard a line stage with JFET input that sounds natural at all. 6H30 unless used with mega current sounds thin. Not sure how Audio Research biases them.

Look at LS7, all tube, only a constant current source for 1st gain stage. All 6922 and no 6H30.

I have not owned either models. Only LS1, LS2B, Reference 1, SP10ii. Current I don't own audio research preamps anymore.

Actually the LS16MKI uses (4) 6922 tubes and is a pure tube
preamp, like the LS7. The LS16MKII uses the (2) 6H30 tubes.
According to the subject title, the OP is asking about the
MKI version

I have owned both versions of the LS16. I found the MKI to
be more tubey sounding and the MKII to be faster, cleaner,
but more solid state sounding. I have never owned the LS7,
but have heard it. It's a pretty nice sounding unit.

I'm not sure the LS16MKI would be that much of an upgrade
over the LS7. If you could sell the LS7 and add a few
hundred dollars to get the LS16MKI, I might consider that,
but I wouldn't pay a whole lot more for it.

You might consider saving up and stepping up to the LS26.

For the record, the advantages of using a jfet input are many but the single most important advantage is the decrease in noise. Comparing the SP-16 an all tube preamp and the SP-17 with its jfet input, you will find the SP-17 is almost 10dB quieter! That is huge. With the phono stage installed it's the difference between having to use a 2.5 mV high output moving coil because of noise, and a moving coil that's in the .7mV range. More cartridge choices and much less noise, therefore a rather substantial difference. The use of the 6H30 tube, because of it greater voltage swing, ( it draws more heater current) greatly improves dynamics and transient performance over the 6922 or the 12AX7. The bottom line is the fact that each person's hearing and audio systems are different, it's best to listen to a preamp, if possible, in your own system in order to evaluate it's performance. There is no right or wrong choice.

Agree with hifigeek regarding the need to have quiet gain for phono stage.
Disagree when it comes to a 15 to 20 dB gain line stage.
But it's just me.