ARC LS25 mkii vs ARC Ref 5se

The LS25 was introduced in 1998, the same year as the Reference 2.  The REF5  was introduced in 2009 and the REF5SE in 2012 probably. I got these data from the ARCDB (Google it). So LS25>REF2>REF3>REF5>REF5SE is a lot of steps up.  I have no doubt the REF5SE will sound better.

I would sure hope there’s a huge difference. I took home a LS 25 MKII when I was last shopping for a preamp, and that preamp didn’t do much for me… didn’t do anything bad but I felt the ModWright LS 36.5 was more engaging at least in my system. I have not dragged home an ARC Reference preamp but have listened to them a lot at local dealership and even there they sound special. I’d be surprised you’d be disappointed if you make the change. 

I currently have a Ref 6SE, prior I had a Ref 5SE and have listened to LS27 and LS28SE.

The Reference series is definitely a step up in sound quality, just like the LS28 SE is a step up from the LS27SE. I’d say the LS to Ref of the same generation is a bigger step than one or two generation steps in the same level. 
 

So after yours is the LS26, LS26SE, LS27, LS27SE… etc. 

The Reference series is cut from the same cloth as the LS… exactly… so same tonal balance, midrange bloom etc, but generally better in all qualitative qualities, noise floor, dynamics, imaging etc.

The decision would must include consideration of your other equipment and future of your system. If you are looking long term, then regardless of your other equipment the Ref would be a good decision. If you are mostly concerned about cost, then maybe an upgraded LS would suffice for you.

It would be very helpful to see your system. This is very helpful for us trying to help. There is a place under your ID to place some quick photos and ID equipment under Virtual systems. You can see mine there.