80/20 principle, 80% of your results come from just 20% of the things you do. First look for the things that you can change that are going to make a big difference, not things that are going to make some 0.0001% difference that you won't even hear.
In this case:
- Speakers
- Cartridge
- Phono preamp
- Turntable
- Source
Would be the things to focus on. Mats, Weights, and all that jazz aren't what you need to be looking at. They aren't going to give you any of the bass improvement you're looking for.
So let's go through those:
- Cartridge: You have a solid cartridge, and I've never heard anyone make any complaints about the bass response it offers. In fact I've heard several people claim it's one of the best cartridges they've heard in that department. Make sure the stylus isn't damaged or worn, but assuming it's not, you're fine in the cartridge department. No changes need to be made here.
- Turntable: Providing it works, keeps speed, etc, it should not for all intents and purposes be having any significant noticeable effect the bass response you're getting, so we can rule out any changes needing to be made here.
That leaves the source, the phono preamp, and your speakers as things where there could be room for improvement.
- Source: You mentioned that you have a VPI cleaner, so we can assume your records are kept in good condition. However, that doesn't say anything for the actual source material itself. Low frequency material requires wider grooves to be cut, which places limits on other information that can be stored and on the overall length of the record - so with many records, some low frequency information is cut off to prevent these limitations. So in some cases you might find the bass response isn't what you're used to if you previously listened to digital - that isn't always the case though, it just depends on how it was cut etc. Try a wider selection of records and see if the bass is more pleasing to your ears on any of them than the ones you've been listening to - if some sound as good as you like, but others don't, then it's an issue with the records and not your system.
- Phono Preamp: Your phono preamp can definitely have an effect on the sound that you're getting, but the effect should be a subtle one, and unless there's something wrong with the phono stage in your receiver it shouldn't be killing your preamp.
Which leaves, the obvious culprit:
- Speakers: Bookshelf speakers generally don't have that good a bass response, period. There are some exceptions to the rule, but even then there's a limitation to how far a 5 or 6" woofer can really go. If you're someone that doesn't care much for bass, then you can go without ever noticing this limitation - but if you like some music where the bass reaches deeper, and with more authority, you'll probably find such speakers on their own will let you down. This is why a lot of people, like myself, choose to pair their bookshelf speakers with a subwoofer - and this is likely the solution to your problem. Find a decent sub, hook it up, and you should find the bass response much more to your liking.
The only other thing I can suggest is to check if your speakers are rear ported (I couldn't find any info) and if they are, position them close to a wall. Depending on the speaker it may sound better or it may sound worse, but there should be more bass. If they are and it helps, see how you feel about the better bass response - is it enough? If so, great, you're sorted. Still not enough? Then look at getting a sub like I suggested.