The silex is over-extracting the coffee during a 12 minute brew cycle. The over-extraction makes the brew darker, but also more bitter and more acidic. Some components of the ground coffee are better left behind in the spent grounds than extracted into the cup (if one seeks best taste).
Many residential brewers are designed to over-extract the grounds in response to consumers under-dosing coffee (and grinding too fine for drip brewing) in their attempts to economize. Scrimping on coffee grinds quantity to save a few cents per pot generally yields poorer cup quality. The exception may be for low quality commercial grade coffee that tastes harsh - an under-dosed weaker brew may yield a more palatable cup.
Since you are accustomed to the over-extracted taste, you may not choose to switch. A faster brew cycle (3 to 5 minutes is optimal) will yield a rich cup with cleaner, crisper, taste that is not harsh and over-extracted (unless the grind is too fine) truer to the taste the roaster intended and describes on the package.
The Bunn brewers can make an excellent cup (they usually have higher brew water temperatures). This type of brewer is designed along "old school" and "specialty coffee" concepts, which use higher ratios of ground coffee to water than many American coffee consumers have become accustomed to. The recommended ratio is 2 tablespoons ground coffee per cup. The basket filter design requires a deep enough bed of coffee for proper extraction - usually an inch to 2 inches deep, depending on the brewer.
If you decide to bail on the better quality Bunn brewer, perhaps a cone shaped filter brewer will give you the over-extracted taste you are accustomed to, while giving you a faster brew time. Most cone filter brewers make a better tasting cup if you make half or 2/3 pot size rather than brewing a full pot and really over-extracting the brew. I also find that a regular drip grind yields better results than the "melitta" grind which is too fine.
Best of luck. Please let us know what you are satisfied with after all this.