Marlebob, why you limit your searches just to Europe? After some reading I think that Lecketon UHA-4 would be a good, very portable, companion.
BTW, it is so obvious and other hand a little bit odd how different tastes are. Marleybob, as I understand you correctly C5 is maybe too warm for yours BA4f but it gives you much fuller sound. For me I would never want to add a warm amp to my BA4r which by definition I would expect is less fuller than yours BA4f because for me BA4r has already full sound:confused:
Moreover, BA4r were compared to Etymotic ER4s...hmm...yes, they have something in common but my initial impressions (although I have to admit that I've listened my BA4r maybe just for 3 hours) are that BA4r have fuller sound and lacks a little bit this treble sparkle which Etys have, so I'm a little bit confused whether they are actually similar.
Despite the above, I'm very pleased with my BA4r. I like the cable very much. I was afraif a little bit that the acrylic CIEM will not be comfortable (until now I only had silicone custom sleeves for my Etys), but for me they are actually comfortable.
Thank you Phil for making this interesting CIEM.