Reference 3A De Capo or Rogers LS3/5 ?

Move up to a larger sized cabinet speaker. The poster that recommended Harbeth is on the right track; consider the various spendors. The Spendor 2/3 is an excellent speaker and works well with a tubed amp of 20 watts or more; well, a quality tubed amp....

The other route you could consider would be to add a subwoofer. I borrowed some Spendor S3/5s for long weekend from a friend and set them up crossed at 70Hz with my REL strata. It worked very well, to the point where the crossover was hard to detect. It added a lot of weight and authority to the sound of the spendors without changing any of the midrange or top end of the spendors. I now run my REL with green mountain audio europas.

Since the REL attaches to the speaker outputs of the amplifier in parallel with your existing speakers, and has an almost infinite input impedance it is an add-on that in no way modifies your existing setup. The Rogers will continue to work over their full range with the REL coming up underneath them. Spendor also makes a subwoofer designed to match their s3/5s that would probably work well.

The only caveat is that I have found that the subwoofer needs to be well out into the room in order to load the bass correctly into the room, but if you can afford the space you can make the Rogers sound like large floorstanders with this method.

Before you jump onto Reference 3A De Capo, you need to understand your room acoustics first.
This particular speaker is rear ported, which means that placement is very important. How far to the wall is critical to the sound.
Rogers is direct firing near field speakers build for studio use. Placement is straight forward and the room acoustics is less critical.
I never like small ported speaker sound. The lower frequency is a bit distorted to my ears. But that's just my preference.