Tubes Recommendation for McIntosh Preamp

Hi,  I recently purchased an used McIntosh 2-chassis C1100 tube preamp.   So far I'm pretty happy with it.    

I'm thinking about replacing the line level stock tubes.  They are 2 12AT7 and 1 12AX7A per channel.   

I'm looking for recommendation from fellow members here.   I would like something on the warm side (definitely not bright sounding), and good solid and tight bass.   

Also I wonder if I need matching.  e.g. do I need 2 matched pairs of 12AT7, with each matched pairs for each channel.  Or do I need matched quad of 12AT7 for both channels.   Same question for the 12X7A.  Do I need them to be matched.   I don't seem to see any information available in the user manual on tube replacement.

Thanks very much in advance!


Also, FWIW, on a C2500 I swapped in NOS Telefunken 12AX7.   Huge  improvement across the spectrum.    

For what it's worth, I own the McIntosh MA352 Integrated Amplifier which uses 2X 12AX7A tubes and 2X 12AT7 tubes.  I believe McIntosh sources from New Sensor but I don't have direct confirmation from the company.  I've been using the stock tubes for five years now without any issues.  The sound is great and I have no complaints.  Recently, I replaced the 12AX7A stock tubes with a matched pair of low micro-phonic 1960s Amperex Bugle Boy tubes for comparison.  I bought these tubes about a decade ago.  I stored them when I sold my tube equipment.  Having heard the stock McIntosh tubes versus the NOS Bugle Boys, the McIntosh tubes sounded better to me.  The stock tubes are more crisp (clarity & imaging), quieter (sound stage), and the bass was significantly tighter.  Additionally, the NOS tubes cost $130 a piece while current issue New Sensor (Russia) cost less.  Needless to say I put the stock 12AX7A tubes back into the equipment.  I do know that McIntosh individually tests their equipment with the stock tubes prior to delivery to ensure the best sound and compatibility.  Save yourself some money; instead of buying NOS tubes, it might be useful to consider premium New Sensor tubes as an alternative.  Cheers!

Thanks very much @wescoman for sharing your experience, Very helpful.

I actually think the current sound is not bad with the stock tubes. I was told the unit was about 1 year old, but I don’t know how many hours did the previous owner put in on the unit,

I have no experience of what a bad tube sounds like. So I thought for my own peace of mind, I would try some new tubes. But it is so good to know that you are running the stock tubes for 5 yeas without any problem. That’s wonderful!

I might just leave it for a while and see how it goes!